Single-choice Early Action is an admissions plan offered by some colleges and universities which requires students to submit an application early, usually in November, and agree to attend that school if accepted, withdrawing other applications from other colleges and universities. Some single-choice early action (SCEA) plans however, like that of Stanford or Dartmouth College, don't allow students to apply early decision or early action to any binding program at another institution, but do not restrict regular action or non-binding early action applications at other schools while you wait to hear from that college's SCEA committee decision.
You should always carefully familiarize yourself with a college's early action agreement policies prior to submission by visiting its official admissions office webpage.