The term breaking in refers to when a puzzle doesn't turn very well, and you begin to solve, or perform movements on the cube with the intention to make the cube turn smoother. You can break in a puzzle by solving it a few hundred times, or using triggers over and over such as (R U R' U'), and then proceed to do that on all sides.
Sanding is an alternative...
- Speedsolving.com How to Break in a cube
- Speedsolving.com What is breaking in?
- Speedsolving.com Lubing a DIY before breaking in??
- youtube.com