| Definition -
Speech or narration that has been modified to show that it is being reported by another person, i.e. pronouns, tenses, etc. have been modified so that the statement conforms to the point of view of the reporter.
1. As opposed to direct speech, which is reported in the form that it was uttered.
(1) "I am the walrus." (direct speech)
(2) He says he's the walrus. (indirect speech)
Oxford English Dictionary - The term's first citation is from 1866:
"In such sentences…the dependent clauses are indirect questions."
(Mason Eng. Gram. (ed. 7) 111)