Created by ACT Inc., the ACT is an entrance exam used by most colleges and universities to make admissions decisions. The idea (in theory, at least) is to provide colleges with one common criterion that can be used to compare all applicants. The weight placed on ACT scores varies from school to school.
The ACT has four sections: English, Reading, Math and Science, as well as an optional 40-minute writing test. Some schools may require the writing test, so be sure to ask before you take it.