The International English Language Testing System (IELTS) tests how fluent you are in the English language. People who take the test take the Academic Module or the General Training Module. The academic one is for people who want to go to university. The general one is for people who want to do other training or want to get work experience. People who want to emigrate to a country that uses English also take the general one.
Most universities in Australia, Britain, Canada, New Zealand and the United States accept the IELTS. Many professional companies do as well.