A college can have several deadlines for first-year applicants. Each one belongs to a plan. Here is what each plan means.
Apply early, hear early, not binding.
A second, later early action round. Not binding.
Apply early and hear early, but you usually cannot apply early to other private colleges. Not binding.
Apply early, hear early, and you must enroll if admitted. Binding.
A second, later early decision round. Also binding.
The standard deadline, with answers in spring. Not binding.
Apply by this date for the best chance at aid or a place; later applications may still be read.
The college reviews applications as they arrive until the class is full.
Early action costs you nothing but a little earlier work. Early decision is a promise, so use it only for a college you want above all others and can afford. Check each college's own page for its exact rules.