Adult contemporary music (AC) is a broad style of popular music, ranging from 1960 's and 1970 's vocal music softrock to today's mainly Ballads with in alternating degree influences from easy listening, soul, Rhythm and blues and rock. The term is also used to play radio stations/radio programs that to describe this music or to catalog. Adult contemporary is rather a continuation of the softrock and the easy listening style that became popular in the 1960s and 1970s with a number of adjustments that the evolution of the pop/rock music  .
Adult contemporary tends lush, soothing and highly polished qualities where the emphasis is on melody and harmonies to accentuate. It's usually melodic enough to attract the attention of a listener and is harmless and enjoyable enough as background music to be able to work well with. Like most pop music, the songs are usually written in a simple form (often Verse-Chorus structure), as well as the use of repeated choruses  .
Adult contemporary is fond of romantic ballads in which one mainly using acoustic instruments (although also bass guitar usually is used), such as acoustic guitars, pianos,saxophones and sometimes a orchestral set. The electric guitars are usually weak and high. Recent adult contemporary music, however, is usually provided with Synthesizers(and other electronic instruments such as drum machines.) 
AC radio stations also play mainstream music, but they will "hip hop", "Heavy metal", on the youth-oriented "hard rock", "teen-pop" music and rhythmic dance music "exclude", because these genres less popular among the target group of these radio stations, which are intended for a mature audience. Radio stations that play music often focus on AC the age group 18-54, also the population group that has received the most attention from advertisers since the 1960s. 
Over the years AC has spawned several sub-genres: "hot AC", "soft AC" (also known as "lite AC"), "urban AC", "rhythmic AC" and "Christian AC" (i.e., a softer type of contemporary Christian music). Some radio stations play only "hot AC", "soft AC" only while other play. There are other stations that play a large number of sub-genres explicitly.For this reason, AC not considered a specific genre in the music, but as a collection of selected tracks by musicians of many different genres.
1960-Early roots, easy to listen[Edit]
Adult Contemporary has its roots in the easy listening of the 1960s, that 70-80% was instrumental and 20-30% vocal mix. Some offered 90% instrumental and a handful of completely instrumental music offered. The Easy listening format, as it was first known, was born of a desire by some radio stations in the late 1950s and early 1960s to continue playing current hits, but still stand out from the "Rock and roll stations".