Tool-Assisted Speedruns (occasionally Tool-Assisted Superplays) or TASes are a subset of speedruns that are created in an emulator with the aid of tools. The goal of a TAS it to play through the game as fast and precisely as possible. The use of tools allows for many strategies and routes not normally possible by a human runner.
TASes are not created to compete with standard speedruns and often times speedruns and TASes share information to help each other improve.
If you want to learn more about TASes and how they're created, visit TASVideos.