AFR (Air-to-Fuel Ratio), EQ (Equivalency Ratio), Stoichiometric (Stoich), and Lambda (l), are all terms used to specify the proportions of fuel and air in the mixture taken in by an engine. Which you see used will depend a great deal on what you are reading, and on the educational background of the person who wrote the material.
In the professional engine-tuning world, the most common terminology is probably lambda, with AFR a close second. EQ tends to be used less often, and in my experience at least, is more often seen in academic engineering literature.
AFR is the term used for the ratio of Air-to-Fuel. By convention, it is expressed as the number of parts of air to 1 part fuel, with only the “air” value written or referenced. That is, a ratio of 12.0:1 is referred to as “12-point-zero” when expressed as AFR, rather than “12-point-zero-to-1”.
EQ is the term used for the ratio of Fuel-to-Air...