The word "cant" can mean more than one thing:

1. Cant is insincere speech, similar to hypocrisy. The difference between the two is sometimes explained thus: the hypocrite is entirely cynical and doesn't even believe the snake-oil he or she is expounding; while the speaker of cant does have conceptual faith in what he or she says—but won't actually be practicing what he or she is preaching.
2. Canting is an old word for punning in heraldry. For example, a person named Connington might have a rabbit (a coney) and a barrel (a tun) on his coat of arms. See Rebus.
3. Cant is often used in instant messaging as a shorter form of the contraction can't.
4. Cant is a term generally used to describe secret languages (cryptolects) used by gypsies, thieves, and others who have a need to communicate freely without necessarily conveying their meaning to a wider audience. It is used sometimes specifically to refer to Shelta, the cryptolectic Goidelic Celtic language of Irish Travellers.