The word "Gospel" originates from the words "good spell" not "god spell" as many people tend to believe. It is the genre of Christian music developed in 19th century. Gospel music usually has dominant vocals. Moreover, it is composed for various purposes e.g. aesthetic pleasure, ceremonial or even as an entertainment product for marketplace. The Gospel music has its roots in the black oral tradition and originates from African American religious experience. In fact the traces of this genre can be found even in 17th century. It utilizes a lot of repetitions, which at first was used to enable ones who couldn't read to participate in worship.
Probably the name "Gospel Song" was first officially introduced in 19th century in 1874 by Philip Bliss who realeased a songbook entitled "Gospel Songs. A Choice Collection of Hymns and Tunes." He introduced a new type of church music which was easier to grasp and easier to sing than the traditional church hymns and it served the needs of mass revivals in the great cities.
The music itself in general is characterized by dominant vocals with strong use of harmony and referencing lyrics of Christian nature. There are several subgenres which include "contemporary gospel", "urban contemporary gospel(black gospel)", "southern gospel" and "modern gospel music". Some of them utilize choirs, use piano or Hammond organ, tambourines, drums, bass guitar and electric guitar.
