The grid displayed in the image demonstrates the composing style called the rule of thumb
rule of thirds
rule of ninths
rule of symmetry

Its called the "rule of thirds"

Explanation:

If you look up "rule of thirds in art" images similar to the one you have will pop up! :)

My teacher always called it the "Grid method" so I was stumped for a second lol.

12-bar blues chorus = a a b