1.nounA backward regression; a reverting back to a worse state.
2.nounA dance move in which the feet are alternately slid back and the heels lifted, giving the illusion of walking forwards while actually moving backwards; later popularly called the moonwalk.
3.verbTo regress; to slip backwards or revert to a previous, worse state.
"He felt better for a little while, before his condition started to backslide."
4.verbTo shirk responsibility; to renege on one's obligations or commitments.
"Rich countries are backsliding on their commitment to agree to new WTO measures to help people in poor countries gain access to affordable medicines. — Oxfam press release, 24 June 2002"