A roast is an event, almost exclusively in the United States, in which an individual is subjected to a public presentation of comedic insults, praise, outlandish true and untrue stories, and heartwarming tributes, the implication being that the roastee is able to take the jokes in good humor and not as serious criticism or insult, and therefore, show their good nature. It is seen by some as a great honor to be roasted, as the individual is surrounded by friends, fans, and well-wishers, who can receive some of the same treatment as well during the course of the evening. The party and presentation itself are both referred to as a roast. The host of the event is called the "roastmaster". Anyone who is honored in such a way is said to have been "roasted".
Also from Wikipedia on 'Comedy Central Roast':
The Comedy Central Roast of Donald Trump was originally taped on March 9, 2011. Roasters included Whitney Cummings, Lisa Lampanelli, Jeffrey Ross, Marlee Matlin (interpreted by friend and business partner Jack Jason),Gilbert Gottfried, Anthony Jeselnik, Larry King, Snoop Dogg, and Mike "The Situation" Sorrentino. Melania Trump, Ivanka Trump, Ice-T, Russell Simmons, John Legend, Lindsay Lohan, and David Foster were in the audience. The roast consisted of jokes toward Trump's hairstyle, his show The Apprentice, and his family. Jokes were also made about Jeselnik's fame (or lack thereof), Matlin's deafness, King's age, and Jersey Shore. Several roasters paid respect to Greg Giraldo, a Comedy Central Roast regular, who died on September 29, 2010. Mike "The Situation" Sorrentino was highly criticized for his performance; as a result, Comedy Central pulled several of his jokes from the television airing of the roast. This roast was dedicated in memory of Greg Giraldo. This was also the first time someone served as roastmaster more than once, as Seth MacFarlane also roasted David Hasselhoff.