Form and Genre are the architecture or music. They are what gives a musical work its shape and to a large extent determine the direction a piece of music takes form its opening to its end. While form and genre are related (and sometimes synonymous – as in the case of the minuet for example) there is a difference between the two.
Musical form refers to the structure of a work. How many sections it has, in what keys those sections are (relative to the main key), or how many times and when a particular section or theme is heard.
When we talk about genre in music we are not referring to the particular style the music is written in (Jazz, Folk, Classical, etc.) but usually a combination of form and other factors. An opera is one genre, a symphony is another. The concept albums of the progressive rock movement could also be considered a genre.
You can read about specific musical forms and genres by following the links below.