Plain English Meaning
When the mind hides something upsetting from itself so the person doesn't have to deal with it. The student doesn't know they're doing it.
Full Definition
A defense mechanism in which a person unconsciously pushes painful, threatening, or unacceptable thoughts, feelings, or memories out of conscious awareness. Because the process is unconscious, the individual is not deliberately choosing to forget — the mind blocks the material on its own to reduce anxiety.
Context Anchor
Seen in Aviation Instructor’s Handbook discussions of student behavior, stress, and emotional responses during training.
Derivation
From the Latin reprimere, meaning 'to press back' or 'hold down.' That image fits well: the mind is pressing uncomfortable material back below the surface so it doesn't have to be faced.