Oldies is a term commonly used to describe a radio format that concentrates on music from a period of about 15 to 55 years before the present day. In the 1980s and 1990s, "oldies" meant the 15 years from the birth of rock n roll to the beginning of the singer-songwriter era of the early 1970s, or about 1955 to 1972, although this varied and some stations chose 1950-1969. In the early 2000s, 1970s music was increasingly included, and early 1980s music is beginning to also be called "oldies", though the term "classic hits" is used to distinguish the "new" oldies (the Generation X oldies) from the "old" oldies (the Baby Boomer oldies).

Oldies tunes are typically from R&B, pop and rock music genres. Country, jazz, classical music, and other formats are generally not considered oldies music, although some of those genres have their own oldies format (for instance, classic country), and a number of songs "crossed over" from country to Top 40. Occasionally the term is used to describe the rare station that includes 1940s music as well, although music from before 1955 (coinciding with the "birth of rock'n'roll") is typically the domain of the adult standards format. However, the term constitutes ambiguity for people who like old dancing music. This format is sometimes called Golden Oldies (after another album series of the same name, which was sold through bulk TV commercials), though this term usually refers to music exclusively from the '50s and early '60s. Oldies radio typically features artists such as Elvis Presley, Chuck Berry, The Beatles (pre-Revolver), The Beach Boys (pre-Pet Sounds), The Supremes, The Four Seasons, and Sam Cooke; as well as such musical movements and genres as doo-wop, rockabilly, rock and roll, Motown, British Invasion, early girl groups, surf music, teen idol singers, and bubblegum pop. Most traditional oldies stations limit their on-air playlists to no more than 300 songs, on the philosophy that average listeners will stay tuned provided they are familiar with the hits being played. The drawback to this concept is the endless repetition of the station's program library. Oldies has some overlap with the classic rock format, which concentrates on the rock music of the late-'60s and '70s and also plays newer material made in the same style as the older songs.

A variation on the oldies theme is classic hits, which provides most of the playlist of oldies with some classic rock with an addition of contemporaneous R&B and pop hits as well, striking a balance between the mostly '70s-focused classic rock genre and the more broad-based oldies format.