What is Challenge ?
Challenge is (noun) 1. a difficult test of someone’s skill or strength etc. The action by the union is another challenge to the authority of the government. to pose a challenge to someone to be extremely difficult to do Getting the piano up the stairs will pose a challenge to the removal men. 2. an invitation to something such as a fight or competition Our team accepted the challenge to play another game. to take up a challenge to agree to fight(verb) 1. to ask someone to prove that he is right When challenged, he admitted that he had seen her get into a car. The committee’s conclusions have been challenged by other experts. 2. to challenge someone to a fight to ask someone to fight you
source: Easier English, Student Dictionary Upper Intermediate Level