TEFL means Teaching English as a Foreign Language. You might also hear it called TESOL - Teaching English as a Second Language. It's one of the best ways for a career breaker to get paid work abroad.
You normally take a course in the UK, before you go away. You can do the course in person or online, full or part-time, intensively or over several months. You can do classroom practice if you like.
You will need the Trinity Cert. TESOL or the CELTA qualification - these are recognised internationally.
Many TEFL course providers offer a job-finding service once you've got your qualification. Some even guarantee jobs.
Learning English can be a very valuable skill to many different kinds of people. Business people, for example, need good English to work with people of other countries (not just English-speaking countries of course). Children in poorer countries with a good command of English have better job prospects than those without. So as well as earning money, you will be bringing your knowledge to your students - and they will benefit from it long after you've gone home!