It is a triathlon
Trisection
If your racing and betting on each others horses its called Racing for Pinks!
The three secondary parts of a triangle are typically associated with one word. They are commonly called the perpendicular bisectors of the triangle.
The cerebrum, brain stem and the cerebellum.
one third = 1/3
That could be called a trilogy, although that may refer to a series of three movies. Then again, if the three "parts" of the movie are all seperate movies (eg. Harry Potter and the Deathly Hallows part 1 and 2 were seperate movies) then three parts of a movie could be called a trilogy.
The three main parts of a clock is called an energy supply, a mechanism for regulating the energy and a way of showing the passing of time
neucles , fatousmousa , gladuos wall
quartiles
The three parts of a lever are the fulcrum (pivot point), load (resistance being lifted), and effort (force applied to move the load). The support of a lever is called the fulcrum.
A story told in three parts -- whether in a book or a film -- is called a trilogy.