The titular
line (or title line) is a line in a film,
book or song which includes the name of the film,
book or song.
eg. In the movie "Limitless" starring Bradley
Cooper, the protagonist (Eddie Morra) explains the effect that a newfound mystery pill has on his intellect. He says, "a tablet a
day, and what I can do with my
day was limitless." This is called a titular line.