Sledging or "Mental Disintergration" as it is also known is the tactic of talking to players on the opposition side (particularily batsmen, as taking on a whole team in the field is never a good idea) with the objective of destroying either their concentration or their confidence/self esteem. Sledging is practised in a large way by the Australian Cricket Team, but most International teams partake in sledging. Sledging can be merely an opposition player talking constantly to the batsman, but has mostly become known as players swearing and questioning their lineage.
Glenn McGrath to Eddie Brandes
GM: "Oi Brandes why are you so fat?"
EB: "Because everytime I shag your wife she gives me a biscuit"
Andrew Flintoff to Tino Best (after Best had attempted a slog sweep towards the pavilion)
AF: "Mind those windows Tino"
Rod Marsh to Ian Botham
RM: "So how's your wife and my kids?"