MashGet

Demo from WikiPedia:

A demo version or demo of a song (shortened from the word "demonstration") is one recorded for reference rather than for release. A demo is a way for musicians to approximate their ideas on tape or disc, and provide an example of those ideas to record labels, producers or other artists. Musicians often use demos as quick sketches to share with bandmates or arrangers; in other cases a songwriter might make a demo to send to artists in hopes of having the song professionally recorded, or a music publisher may need a simple recording for publishing or copyright purposes.

Many unsigned bands and artists record demos in order to obtain a recording contract. These demos are usually sent to record labels in hopes that the artist will be signed onto the label's roster and allowed to record a full-length album in a professional recording studio. However, large record labels usually ignore unsolicited demos that are sent to them by mail; artists generally must be more creative about getting the demos into the hands of the people who make decisions for the record company.[citation needed]

Read more on WikiPedia