What does "plum job" mean?

[Tamta]

He is very lucky to have got himself a ......... job.

(a) pear
(b) banana
(c) lemon
(d) plum

He is very lucky to have got himself a plum job.

Correct answer: (d) plum

Your answer was: incorrect

Could you explain to me,please:
What does "plum" mean in this case?
What is "plum job?"

Thanks in advance

[Jamie (K)]

A "plum job" is a very easy, pleasant job that pays well. Sometimes it means a very good job that most people can't get.