Each school at all levels (D1, D2, D3) may have it's own admission policies. Schools with some form of Early Decision (or Early Action) usually offer one of theree types.
ED exists at many schools. The applicant applies early to just one school and gets a decision early. If accepted, the student will withdraw all other applications and agrees to attend the school (no changing your mind or waiting for the best financial aid offer).
Another option at some schools is Early Action (EA). EA is not binding, you apply early and get a decision early, but can still apply to other schools. A third option available at many schools is Single Choice Early Action (SCEA). Like EA, it is not binding, however you may only apply to one school early. If accepted, you may still apply to other schools.
DIII and the ivies often use ED or SCEA as a substitute for the NLI. Both parties commit early, though there is no scholarship contract.