What is the meaning of Flunk?

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

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

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.)

Source: wiktionary.org