Simplify the following text for a Grade 11 native English-speaking person.
Original: Princeton University 's Wordnet dictionary states that `` progressive rock , art rock '' are `` a style of rock music that ( came out ) in the 1970s ; associated with attempts to ( mix ) rock with jazz and other forms . ''
Simplified: The concept of `` art rock '' has also sometimes been used to refer to the `` progressive rock '' bands which became popular in the 1970s . Allmusic states that `` Progressive rock and art rock are two almost interchangeable terms describing a mostly British attempt to elevate rock music to new levels of artistic credibility . ''