What is "tyranids"

In the fictional universe of Warhammer 40,000, the Tyranids are a race and a playable army in the tabletop miniatures wargame.

The Tyranids are aliens from outside the galaxy who have come to devour all life, one planet at a time. Though they collectively possess a powerful intelligence, they cannot be reasoned with. Tyranids come in diverse forms, each individual having been engineered to fulfill a specific role. All of their technology is biological, named in the Universe as biomorphs due to their components being alive.