It is the name of a 2008 movie, starring Leonardo DiCaprio, and also a 2007 novel, written by David Ignatius.
Well, titles of creative works are often... creative. There's "body of lies" meaning "a collection of lies", as in @Khan's answer, and then there's meaning in the context of the work.
Wikipedia says this about the novel:
Referencing the real (and highly successful) Operation Mincemeat, "Ferris's plan is inspired by a masterpiece of British intelligence during World War II: He prepares a body of lies, literally the corpse of an imaginary CIA officer who appears to have accomplished the impossible by recruiting an agent within the enemy's ranks.
So, in context of this novel "body" in "body of lies" means "corpse".
A body of something means a large amount or collection of something. Informally, "a body of lies" means a pack/load of lies.