Adult oriented rock (AOR) is a music genre that is characterized by a rich, layered sound, slick production and a heavy reliance on pop/rock hooks (rateyourmusic.com). This genre had its heyday in the early 1980s, but luckily it never really left since.
The genre most defining bands are Journey, Foreigner, Toto and Survivor.
Toto‘s 4th album Toto IV (1982), not only proofs that at least some AOR bands at a certain point in time were not awfully inventive in the naming of their albums, but is also a true classic in the genre, that’s a perfect link between the sheer perfection and melodic quality of West Coast music and the power of Rock (courtesy of Steve Lukather).
Other well known bands that are usually classified as AOR are REO Speedwagon (read more about their best and most succesful album here) and Survivor, that reached astonishing artistic and considerable commercial heights with their 5th album, Vital Signs (1984), that features excellent new singer Jimi Jamison and saw songwriting tandem of Jim Peterik and Frankie Sullivan at its peak. All songs on the album are classic AOR/Melodic Hard Rock.
Less well known bands
From the early 1980s on an overwhelming amount of bands followed in the footsteps of these bands. So there’s a lot more to discover. Some good starting points: this list of albums that were reviewed in the legendary AOR Classics magazine, Glory-Daze‘s extensive set of reviews, the list of Rock Report‘s all time favorites or a collection of articles from 1980s Boulevard magazine.
In the US AOR orginally stood for Album Oriented Rock, a sub genre of Symphonic Rock, that was called Pomp Rock in the British music press. More on that specific sub genre is found here.