The Usenet newsgroup rec.games.roguelike.nethack is very helpful and informative for Nethack players, but some of the terminology can be confusing for the uninitiated. This glossary aims to define cryptic terms such as the "protection racket" which are bandied about on the newsgroup. If you have any comments, additions or corrections, please feel free to email me. For abbreviations and acronyms such as YAAP (Yet Another Ascension Post) and AoLS (Amulet of Life Saving) please see Dylan O'Donnell's helpful list.
Note that this document contains spoilers and that many of the strategies described herein are controversial.
The ascension kit is the equipment which Nethackers consider indispensable for winning the game. Players will generally use the Castle wand of wishing to fill any holes in their ascension kit. Ascension kits normally include sources of magic resistance and reflection, speed boots and a blessed bag of holding.
Heading for the castle as quickly as possible (perhaps by digging or level teleportation) so as to get the wand of wishing early. This strategy is most useful to reasonably tough characters who have magic resistance but lack some useful items.
An efficient way of cleaning out shops. First build up credit by dropping your gold in the shop and having your pet steal it back. Then convert the credit into cash (at less than 100% efficiency) by repeatedly buying the shopkeeper's items from your credit, starting with the most expensive, and selling them back for cash. Repeat as needed until you own all the shopkeeper's money and goods. Kent Paul Dolan has posted a much more detailed description of how to credit clone.
Nurse dancing is allowing a nurse to hit you while you are naked and weaponless, which will heal you and may increase your maximum HP. One way to maximise the benefits is to reverse genocide nurses in a locked room on a no-teleport level (nurses teleport away after healing you).
Reaching Minetown with as low an experience level as possible (ideally while still at level 1) so that you can buy protection cheaply. This is a highly risky strategy which, even in the hands of an expert, kills about 20% of the characters who attempt it. It works best for Gnomish Healers because they start with a lot of money and the dwarves and gnomes in the Mines will be peaceful to them. This thread has more discussion of how to do the protection racket.
Puddings will split in two when hit with an iron weapon. Pudding farming is a way to exploit this by hitting puddings with a wimpy iron weapon (or non-weapon such as an orcish helm). It involves killing some of the puddings for their corpses (which can be eaten or sacrificed) and their randomly generated "death drops", while leaving others alive to continue the process. This thread has more information on pudding farming.
Many Nethackers consider pudding farming to be abusive and believe that the game should impose limitations on it.
Rerolling means that if you don't like the stats or items that your character starts with, you immediately quit and start a new character. Although this is a legitimate part of some other games (such as Angband), it is generally considered to be abusive in Nethack. It is also an ineffective way to learn the game, as keeping weak characters alive is an important part of being a skilled Nethacker.
Wraith luring is the practice of leading wraiths off levels with graveyards to increase the chance that they will leave corpses. It is less useful now than it used to be because the Castle is now classified as a graveyard level.