The verb "to blaspheme" means to speak impiously or contemptuously of God or sacred things. The noun "blasphemy" describes the act, which may entail impious or profane speaking or behavior. It may, in more general terms, be an act or irreverence towards something that is considered sacred.
The words "blaspheme" and "blasphemy" are derived from the Greek word "blasphemeein," meaning "to speak ill." This is also the etymological origin of the verb "to blame" and the associated noun. An example of blasphemy would be when John Lennon of The Beatles claimed that his pop group was "more popular than Jesus."