The "End", the finale or grand finale. The last lap, last part, final league, last gasp or last breath.
The final part of a play could be called several things: Denouement The finale The epilogue The final act.
A final part can be called a post script, or as an abbreviation, a PS.
"Final" can be both a noun and an adjective. As a noun, "final" refers to the last or concluding part of something. As an adjective, "final" describes something that is last or ultimate in a series.
Dénouement
In Final Fantasy VIII, the spaceship was called Ragnarok.
epilogue
The home stretch
Home stretch
The part of something is called a component. It is a piece or element that makes up the whole of an object or system.
A tenant farmer, otherwise referred to as a share cropper, farms in exchange for part of the final crop.
A small piece or part of something like a piece of glass is called a shard.
The home stretch is the final part of the horse race. This is when the last few lengths around the final turn are ran.