The Most Frequently-used Acronyms

CALL = Computer Assisted Language Learning
EFL = English as a Foreign Language (Studying English in non-English-speaking countries)
ESL = English as a Second Language (Studying English as a non-native speaker in a country where English is spoken. Depending on where you are from,the term ESL may be more inclusive and includes EFL. For some people the reverse seems to be true.)
L1 = "Language 1" = the student's native (primary or first acquired) language.
L2 = "Language 2" = the language being learned or studied
TEFL = Teaching English as a Foreign Language
TESL = Teaching English as a Second Language
TESOL = Teaching English to Speakers of Other Languages (It is also the name of an association, Teachers of English to Speakers of Other Languages, Inc.)
TOEFL = Test of English as a Foreign Language
TOEIC = Test of English for International Communication

Commonly-used Acronyms

5W's = Who, What, Where, When and Why
CBI = Content Based Instruction
EAP = English for Academic Purposes
ELL = English Language Learner
ELT = English Language Teaching (or sometimes Training)
ESOL = English to Speakers of Other Languages (Note: ESL and EFL are often used interchangeably. This acronym is an attempt to make a generic term and then assign more limited meanings to ESL and EFL.)
ESP = English for Specific Purposes / English for Special Purposes
FLT = Foreign Language Teaching
IEP = Intensive English program
IPA = International Phonetic Alphabet (or Association)
LCD projector
LEP = Limited English Proficiency (or Proficient)
LL = Language Lab
NNS = Non-Native Speaker
NS = Native Speaker
OHP = Overhead Projector
SLA = Second Language Acquisition
TPR = Total Physical Response

Other Acronyms Related to TESL

BE = Bilingual Education
CALLA = Cognitive Academic Language Learning Approach
CALP = Cognitive Academic Language Proficiency
CELTA = Certificate in English Language Teaching to Adults
CLL = Community Language Learning
CLT = Communicative Language Teaching
CPE = Cambridge Proficiency Examination
EAP = English for Academic Purposes
ELL = English Language Learner
ESP = English for Special (Specific) Purposes
EST = English for Science and Technology
FEP = Fluent English Proficient (or Proficiency)
FES = Fluent English Speaker
GTM = Grammar Translation Method
LEP = Limited English Proficient (or Proficiency)
LES = Limited English Speaker
LMS = Language Minority Student
LSP = Languages for Special Purposes
MLAT = The Modern Language Aptitude Test
NEP = Non English Proficient (or Proficiency)
OHP = Over Head Projector
SLA = Second Language Acquisition
STT = Student Talking Time
TEP = Transitional English Proficiency
TL = Target Language
TPR = Total Physical Response
TSE = Test of Spoken English
TTT = Teacher Talking Time
TWE = Test of Written English
VESL = Vocational English as a Second Language

Associations

BC = British Council
NCTE = National Council of Teachers of English (United States of America)
IATEFL = International Association of Teachers of English as a Foreign Language (United Kingdom)
MLA = Modern Language Association
OCR = Office of Civil Rights
USIA = United States Information Agency
USIS = United States Information Service
IATEFL = International Association of Teachers of English as a Foreign Language
ACTFL = American Council on the Teaching of Foreign Languages (United States of America)
APA = American Psychological Association