Depending on context, either an abbreviation of popular music or a term for a subgenre of it.
The subgenre of pop is perhaps the most widely crowd-pleasing form of popular music. As a rule, pop music features simple, memorable melodies with catchy, singalong choruses, and instrumentally features heavy use of synthesiser backing. It is instantly accessible to even the musically uninitiated. Successful pop music (and successful pop music is usually measured in terms of its commercial success without any pretence to broader artistic goals) is usually performed by charismatic performers who may or may not be musically talented but who look attractive and may dance well. Songwriting and arranging is performed by anonymous but often well-paid producers.
The image of pop performers is often regarded as being as important as their actual music. Consequently, pop performers and their managers make elaborate efforts to project the desired image through their clothing, video clips, manipulation of the popular press, and similar tactics. Indeed, many pop acts are formulated around achieving the desired image, with music considered later. Boy bands and girl bands are particularly carefully organised in this manner, with members chosen and groomed to fill certain stereotypes to appeal to different personalities of fan.
A particular style of song particularly associated with the pop genre is the love ballad, a slow song in which the performers sing usually highly sentimental songs about various aspects of romantic love.