Current Church law specifies 'meat' as follows:
The law of abstinence forbids the eating of meat (of mammals and birds). However, eggs, milk products, fish, shell fish, and all other cold blooded animals may be eaten, e.g. snails. Similarly, small quantities of condiments (i.e. flavourings) made from animal fat, other meat-derived products, and meat broth may be eaten (note, however, that a meat soup with large chunks of meat would seem to move from the category of broth to that of forbidden meat).
A more detailed analysis follows below:
Note: some argue that Paenitemini III.III.1's statement that "the use of meat" is forbidden thus maintains the pre-Conciliar prohibition of meat broth, gravy, meat juice, bone marrow, fat, blood, lard, soup cubes made from meat products etc (though gelatine made from animal products, and other meat extracts that have lost the taste of meat were always considered permitted). These just-mentioned products were forbidden in the old Code of Canon Law and are thus listed as forbidden in the older Manuals. However, as Jimmy Akin convincingly argues, and as indicated further below, given that the opinion that these items are still forbidden can only be seen as a law of dubious validity, such an opinion it does not bind: " A doubtful law does not bind" being a standard principle of classical Manualist morality, as still expressed in Canon Law 14.
Sources:
“The law of abstinence forbids the eating of meat, but eggs, milk products, and condiments made from animal fat may be eaten. Fish and all cold blooded animals may be eaten, e.g., frogs, clams, turtles, etc”. In Latin:"Abstinentiae lex vetat carne vesci, non autem ovis, lacticiniis et quibuslibet condimentis etiam ex adipe animalium." (Pope Paul VI,Paenitemini, III.III.1 (1966))[This text of Pope Paul VI is cited as currently in effect by Eds. John Beal, James Coriden, Thomas Green, New Commentary on the Code of Canon Law (New Yrk: Paulist Press, 2000), p.1447, John Huels, The Pastoral Companion. A Canon Law Handbook for Catholic Ministry, 3rd ed (Quincy, Ill: Franciscan Press, 1995), p.325, and Eds. E.Caparros, M.Theriault, J.Thorn, Code of Canon Law Annotated (Montreal: Wilson & Lafleur, 1993), p.772.]
“By Condiment is meant that which is taken –whether liquid or solid –in a small quantity with food to make it more palatable.” [Henry Davis, SJ, Moral and Pastoral Theology Vol 2, Heythrop Series II, 4th edition (London: Sheed and Ward, 1945), pp.435-6].
Concerning the argument that meat broth is permitted on days of abstinence:
In the old 1917 Code of Canon Law meat broth and other things derived from meat were prohibited by the phrase 'ius ex carne' or 'iureque ex carne'. The 1966 regulationPaenitemini, III.III.1 removed this phrase and thus seems to permit meat broth and other meat-derived products.
Describing what was forbidden by the 'ius ex carne' clause in the 1917 code, Cameron Lansing writes, "Canon 1250 of the former code (1917) stated that the law of abstinence prohibited meat (carne) and soup or broth made from meat, but not however of eggs, milks, and any sort of condiment derived from animal fat. (Abstinentiae lex vetat carne iureque ex carne vesci, non autem ovis, lacticiniis et quibuslibet condimentis etiam ex adipe animalium.) Ius ex carne is broth or soup made from boiling meat or bones (with marrow flesh). Bouillon crystals or cubes are made in this way. So both broth and reconstituted bouillon would be prohibited. Condimentum ex adipe (from fat) is a seasoning. Fat is distinct from from flesh tissue. The use of beef lard in cooking biscuits or various matas would have been permitted in my opinion. (The use of lard in preparing fish and vegetables at all meals and on all days was allowed by indult, 3 August, 1887.) Jello involved the boiling down of hooves and bones, so it would have been permitted. A gravy of chicken fat would also have been permitted. Clearly carne includes the flesh of mammals and poultry. It does not include amphibians, reptiles and insects."
Jimmy Akin's blog convincingly argues here and here that meat broths are allowed in the new code.
"The law of abstinence forbids the eating of meat, but not of seasonings made from animals fat or meat broth... The law of abstinence obliges all who have completed their fourteenth year until the end of their life (canon 1252)"( Karl H. Peschke, Christian Ethics, Vol 2, revised edition (Evesham: John F. Neale, 1997), p.178, Pechke cites an article to justify this opinion about broth).
T.Cunningham argues that "The prohibition of meat soups on Friday is revoked by the Constitution Paenitemini, interpreted in the light of cn 22 [concerning the manner in which new law surplants old, numbering of 1917 code]. The Constitution covers anew the whole field of legislation on fast and abstinence, and, while repeating verbatim the law of cn 1250, omits the phrase 'iureque ex carne'" (T. Cunningham: Meat Soups on Friday, as summarised in Canon Law Abstracts 19 n.1 (1968),p.71). Although Cunningham states that 'meat soup' is permitted he seems to actually be referring to meat broth. Meat broth is made from meat but no longer actually contains meat: Jimmy Akin thus talks of "soup from meat" as being permissible rather than saying that "meat soup" is permissible. Many if not most non-English countries have much thinner broth-like soups than we enjoy in this country and so the permitted soup probably does not envisage a thick meaty British stew-type soup, or a chili-con-carne soup, both of which would have large chunks of meat and would thus, in my opinion, not be permissible on a Friday.
None of the above commentaries argue for on the permissibility of meat soup with chunks of meat in it.
What was forbidden in the 1917 Code but not the 1966 Constitution:
As already noted, the 1966 Constitution Paenitemini gave a less restrictive abstinence law to the one that was found in the 1917 Code. As Jimmy Akins explains, the 1917 Code forbade the use of many meat derivatives as well as the use of meat itself. As a consequence the older Manuals of moral theology forbade many things, as follows:
“By flesh meat is meant... blood, lard, broth, suet, the marrow of bones, brains, kidneys [but not] condiments made from animals fats]”[Dominic Prummer, Handbook of Moral Theology (Cork: Mercier Press, 1956), p.226].
“The prohibition extends only to the flesh of mammals and birds, including the fat, blood, marrow, brains, heart, liver etc. Lawful foods are fish, frogs, turtles, snails, mussels, clams, oysters, crabs etc. ... Likewise lawful are margarine, and meat extracts that have lost the taste of meat or broth, e.g. gelatine; likewise gelatine products of animal origin, but not soup cubes that contain meat ingredients.” [Heribert Jone, Moral Theology, 15th edition, trans. Urban Adleman (Cork, Ireland: Percier Press, 1956), p.264]. Meat soup, meat juice, and gravy are forbidden by abstinence from meat [Ibid; T.Lincoln Bouscaren SJ and Adam Ellis SJ, Canon Law. A Text and Commentary (Milwaukee: Bruce Pub, 1946), p.636].
“By Condiment is meant that which is taken –whether liquid or solid –in a small quantity with food to make it more palatable... Jellies which are made from animal bones are not meat. Lard... dripping, and also suet” can be condiments, but a quantity of suet that is large enough that it can no longer can be properly seen as a condiment is thus excluded [Henry Davis, SJ, Moral and Pastoral Theology Vol 2, Heythrop Series II, 4th edition (London: Sheed and Ward, 1945), pp.435-6].
Note: Modern ‘stock’ (whether labelled vegetable or meat) varies as to whether it is actually vegetarian or made from those parts of animals flesh that would have qualified it as ‘meat’ in the 1917 Code -regardless, stock is now permitted in the current Code.
Concerning fasting rather than abstinence, note: "[Tag-At] comes to the surprising conclusion that liquids which have nutritive effect (such as milk, broth, eggs) break the Good or Ash Wednesday fast, but alcoholic drinks do not"(D.Tag-At: Questions on Fasting and Abstinence, as summarised in Canon Law Abstracts 79 n.1 (1998),p.72).