Plain English Meaning
FOI is the part of instructor training that teaches you how to teach. Before you can be tested as a flight or ground instructor, you have to pass a separate written test on how people learn, how to communicate clearly, how to plan a lesson, and how to evaluate a student.
Full Definition
Fundamentals of Instructing (FOI) is the body of teaching theory and technique that an applicant must master to become an FAA-certificated flight or ground instructor. It is tested by a dedicated FAA knowledge test (the FOI test) covering subjects such as the learning process, human behavior, effective communication, the teaching process, assessment, instructor responsibilities, planning instructional activity, and . A passing FOI test result is a prerequisite for the (CFI) and Ground Instructor , unless the applicant already holds a teaching credential that qualifies for an exemption.