What's a cover note for a CV? [closed]

I sent my CV to get a job into one company. But they rejected it.

The reason was: "Please do not send your CV without a cover note."

English is not my native language and it is hard for me to understand what cover note means. What is it?

Hmm. ODO doesn't help much.

cover note
a temporary certificate showing that a person has a current insurance policy.

However, cover letter is more helpful, and even provides a suitable example:

a letter sent with, and explaining the contents of, another document or a parcel of goods:
you will need to write a covering letter to send with your CV

You are being asked not simply to send your CV, but attach it to a letter (or note) explaining why you are sending it.