Definition
Bond cleavage is the breaking of a bond. The 2 classifications of bond cleavage are homolytic and heterolytic bond cleavage depending upon whether the bonding electron pair may be split evenly or unevenly respectively, between the products.
Explanation
Bond cleavage usually occurs in reactions in which the carbon skeleton is reduced. The cleavage can happen either homolytically or heterolytically. The former results in a cleaved C-C bond, in which both carbons receive one electron. The latter results when a cleaved carbon retains both the bonded electrons.
For Examples, see Homolytic Bond Cleavage and Heterolytic Bond Cleavage