English definition of “challenge”
DIFFICULT [C, U] › something that is difficult and that tests someone's ability or determination: Finding a decision that pleases everyone is the challenge which now faces the committee. It was the element of challenge which attracted me to the job.
INVITATION [C] › an invitation to compete in a game or a fight: I'm sure Paul will race you. He never refuses a challenge.
DISAGREEMENT [C] › an expression of disagreement with ideas, rules, or someone's authority: a challenge to the authority of the President