A flare was a device that became intensely bright when lit.
In the 1970s, while in the London Underground, the Brigadier used flares to ward away a triceratops while the Third Doctor prepared charges to destroy the area. (TV: Invasion of the Dinosaurs)
On Dido, Barbara Wright used a flare gun to kill Sandy when she believed the creature was about to attack Vicki. (TV: The Rescue)