In literature, music and other arts during their existence has developed various kinds of works. In the literature, for example, novel, Novella, short story, poetry - poem, sonnet, ballad; in fine art - landscape, portrait, still life, and in music - Opera, Symphony... Sort of works within a single art called the French word genre (genre).
Not all musical genres emerged at the same time. Opera, for example, born in Italy in the late sixteenth century, and the symphonic poem was created in the mid-nineteenth century, Franz Liszt.
During its existence of different genres varied greatly, but all retained their basic features. So, Opera is a work for musical theater, which has a plot, is placed in the scenery and is performed by actors, singers, and orchestra. Not to be confused with the ballet or Symphony. But Opera are different: historical, heroic, comic, lyric... they All have their characteristic features, although belong to the same Opera genre. And then, when we need to clarify what kind of Opera in question, we again but in a more narrow meaning of the word, use the term genre. We say: the genre of the lyric Opera, the genre of musical drama, the genre of epic Opera... Within the General concept (genre) vocal music we distinguish between the genres of romance, songs and so on
There is this term has another meaning. Maybe you had to hear about the artist say he was a genre painter. This means that the artist creates paintings of everyday scenes. These paintings were made, for example, V. Perov. From painting the word genre in that the value passed into other art, including music. If we are talking about some work: "there are genre scenes", it means that the composer has introduced a song, dance or March.