Lemon is often the "secret" ingredient that elevates the overall taste of a dish that you can't quite identify. You can find a lemon variety that fits in just about any dish, too. For example, Meyer lemons work everywhere regular lemons do but you can also use them in fruit salads, lemonade, chutney and jams. Eureka and Lisbon lemons, or common bitter lemons, work best as a go-to fruit for dressings, marinades and any dish that needs a pleasant tartness.
Examine the skin color. If the lemon's skin has an orange cast, then it is a Meyer Lemon. However, if it is bright yellow then you will need to examine other aspects to determine what type of lemon you have.
Examine the skin texture. If the skin is very thick and pitted, meaning that is has significant holes in it, then you are likely dealing with a Eureka lemon. These are very juicy and grown commercially. If you bought your lemons at a grocery store, then you almost certainly bought Eurekas. Lisbons have smoother skin that is slightly "grainy" and tend to taper off to a point at one end.
Factor in where you bought the lemon. Eureka lemons are grown commercially and available in chain grocery stores everywhere. Meyer lemons, while a gourmet item, are most often available home grown in California. You may find Limettas in home gardens in the United States or in India and the Mediterranean, while Lisbons are generally found at produce stands in Florida.
Taste the juice. If the juice has a sweet taste with very little bite or sourness, then the lemon is probably a sweet variety. It may be a Limetta, which is a hybrid of the Mexican Lime, or possibly a Meyer Lemon. Both of these lemons are actually mixed fruits. The Meyer Lemon or "Improved Meyer" is actually a cross between an orange and a lemon. If the juice is mostly sour, then you probably have either a Lisbon lemon or a Eureka lemon and you will need to investigate further before identifying the fruit.
Count the seeds. Lisbon lemons are seedless. The other types of lemons tend to have at least a few seeds.