Basic definition is - music used to worship God. The definition can be extended to - music created by Christians.
History of music
To learn about the history of traditional and modern music, you can read a series of articles on Christian history of music, about development of music from early chants to EDM, and what the church had to do with it.
What is worship music?
People often associate worship music with a particular genre of music. Throughout church history, as new music was developed, that genre changed. Just 50 years ago, worship music was associated with hymns of classical music origins. Today, a large number of people associate a form of rock music with worship music. But does worship music necessarily involve several guitars and an accoustic drum set? We think not. We all are different. And just like everyone's voice is different, the style of music we can use to worship God, can be different. At IntelliChristian!, we hope to open doors to diversification of Christian music. From descriptions of heaven that come to us from people who had out-of-this-world experiences, we find out that the number of genres of music we have on earth, is incredibly small compared to music of heaven. With explosion of music in the 20th century, we are only scratching the surface of God's music.