Depending on the conext in which you have heard the phrase - 'toasting' is the term given for an 'MC' who is delivering a rapid rhyme, usually in Jamaican patois, through a microphone, accompanied by a dub reggae record, or 'slate'. Toasting is common and popular at reggae parties, and good 'toasters' are popular additions to an evening. The 'toaster' is a forerunner of the modern rap artist prevalent in r 'n' b and soul music.