It simply means Engineer in Training. It is a body in the United States that is charged with the responsibility of certifying a person after the successful completion of the two requirements:
Completed and passed the National Council of Examiners for Engineering and surveying test on the FE (Fundamentals of Engineering) exam. After completing the examination and passing well, a person is normally awarded an EIT (Engineer-in-training) or an EI (Engineer intern). The state board is the one responsible for this particular task. These two awards, i.e., EI and EIT, differ with a specific state. Engineer Intern could also mean that a person is working as an intern but still a student in college.
Completed a 3-year program in post-secondary school. This program is accredited and confirmed by the board. The EIT does the work of designing being supervised and directed by a Professional Engineer. The Professional Engineer is responsible for stamping, designs sealing, and providing public services.