The term 'mainstream rock' can be replaced with several other synonyms depending on the context. One of the popular synonyms is 'classic rock' which refers to rock music from the 1960s to the 1980s. Another synonym is 'arena rock' which is used to describe rock music that is appealing to large audiences and often played in large arenas or stadiums. 'AOR' which stands for 'Album-oriented rock' is another synonym that was used to describe a radio format that played rock music from popular albums. Additionally, 'radio rock' or 'top 40 rock' are also synonyms that refer to popular rock music tracks that are played frequently on mainstream radio stations.