The difference is in the taste. They both have a bitter tang to them, but lemons, I can’t imagine anyone eating just on their own. A lime, as long as it’s ripe and if you have a taste for them, could be. (Although, about the only thing other than desserts and 7-UP that I can think of that they really get used for is either to mix with drinks or for sucking on with tequila.) But trust me, they’re different fruits.

The best way to learn the difference would be to taste-test something like a Key Lime Pie and Lemon Meringue Pie. You should be able to tell the difference by that alone.

“Lemons

Lemons, scientifically known as Citrus limon, are more commonly known as the fruit that evokes images of sunshine and the sweet smiles of children standing roadside at their homemade lemonade stands.

Lemons are oval in shape and feature a yellow, texturized outer peel. Like other citrus fruits, their inner flesh is encased in segments, with the average lemon having eight to ten.

While most lemons are tart, acidic and astringent, they are also surprisingly refreshing. The two main types of sour lemons are the Eureka and the Lisbon. The Eureka generally has more texturized skin, a short neck at one end and a few seeds, while the Lisbon has smoother skin, no neck and is generally seedless. In addition to these sour lemons, there are also some varieties that are sweet in flavor. One notable example is the Meyer lemon that is becoming more popular in both markets and restaurants.

Limes

Limes are a small citrus fruit, Citrus aurantifolia, whose skin and flesh are green in color and which have an oval or round shape with a diameter between one to two inches. Limes can either be sour or sweet, with the latter not readily available in the United States. Sour limes possess a greater sugar and citric acid content than lemons and feature an acidic and tart taste, while sweet limes, which lack citric acid content, are sweet in flavor.

There are two general varieties of sour limes available, the Tahitian and the Key. Among Tahitian limes are the egg-shaped Persian and the smaller, seedless Bearss. Key limes, famous for the pie bearing their name, are smaller and more acidic than the Tahitian variety.”

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=27

Lemons are yellow.

they differ by flavor, size, and acidity. They are as different as oranges and grapefruits.