Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
The "provirus" is the form of the virus which is capable of being integrated into the host genome.
In the case of HIV it means the DNA "copy" of the HIV genome (remember that HIV normally carries its genes around as RNA), spliced into the host cell's DNA. As far as the host cell's cellular machinery is concerned, this extra DNA is no different from the other DNA, and so the cellular machinery which transcribes genes for protein production, and the regulation which occurs because of genetic interactions, will work with the proviral DNA as well as with the host's DNA.