Meaning

• Of a student, to fail a class; to not pass.

  "He flunked math, again."

• Of a teacher, to deny a student a passing grade.

  "Unsatisfied with Fred's progress, the teacher flunked him."

• To shirk (a task or duty).

• To back out through fear. (Commonly in the phrase 'flunk it', the 'it' referring to a specific task avoided; sometimes without specific reference describing a person's attitude to life in general.)