What does a bad opple idiom mean?

The correct spelling should be: bad apple.

Bad apples mean: bad people.

There are many such idioms in English, which cannot be translated literally.

For example:

big shot

dirty joke

A timid boy

A white day is an auspicious day and a happy day.

new hand

A harmless lie

A useless thing

A dark future, a hopeless future

A comfortable life, a comfortable life

A cold welcome

A cool fish shameless person

The life of a dog is worse than that of a pig's dog.

A cat with money

A fish out of water is like a fish out of water, a little uneasy.