Slither.io rides the wave of the Agar.io's huge success by adding to it the concept of the famous snake game, ie not colliding with the tail of another player.
To stay ahead of your opponents, you can accelerate at any time by clicking the left mouse button.
You will lose some length but will be able to absorb another player and thus grow longer.
Like its famous predecessor, the goal of Slitherio is of course to become the bigger snake in the game.
See also: Agario