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The definition of a challenge is an act of rebellion against someone or something. An example of challenge is an employee questioning the actions of their supervisor in a meeting. A challenge is defined as a demand for proof or an invitation to participate in a competition. An example of challenge is a guard asking for identification.
Challengeâdechallengeârechallenge (CDR) is a medical testing protocol in which a medicine or drug is administered, withdrawn, then re-administered, while being monitored for adverse effects at each stage.