Short for "English as Second Language", the term actually refers to *people* who use english as their second language. These people are often falsely thought of as morons, or generally a person of lower degree/intelligence. They often use their own version of English, mixing in some of their own words or their first language's grammar, especially when talking to other ESL, even more so when the other ESL's first language is the same as his own (when they are speaking English to each other for whatever weird reason, that is.)
Generally ESLs can understand English decently, especially when an ESL version is spoken by another ESL. Their first languages needn't be the same, but it would help even more.
Between the english-speaking community, however, it has a derogatory meaning.

1. Blue Monday is the most depressing day of the year, calculated by Dr. Cliff Arnall, a researcher at the University of Cardiff's Center for Lifelong Learning.
Factors used to calculate the date included weather conditions, debt level, time since Christmas, time since failing our New Year's resolutions, low motivation and feeling the need to take action.

In 2005 the date was calculated as January 24th, in 2006 it was January 23rd, and in 2007 it was January 22nd.

2. A song by the hard rock band Orgy from their album Candy Ass.

Electronic Sports League, mostly known along the European gaming community. An online league where players from all over Europe can compete in. See www.esl-europe.com

an acronym for "english second language", used to describe situations when the misuse of the english language can be advantageous to the person who conveniently exhibits diminished command of the english language yet remains above reproach.

The ESL is a group of hard re's (apart from Ollie and Greevzy) that play in a competitive 8 square league. The league contains 29 retards with one of them missing chromosomes so 28.5 retards that all fight for the glory of winning and taking home 7 points.