There are three aspects of music. These are harmony, melody and rhythm. Harmony covers things such as chords and when more than two notes are being played at the same time. Melody covers riffs, lead ideas, and anything that you can hum. Rhythm is pretty self-explanatory.
The Complete Guide To Improving Your Rhythm With Sub-Divisions

“Drummers view of the show” by Matt Deavenport, licensed under CC BY-ND 2.0.
In this popular YouTube video I created a few years ago, I talked about how to play a variety of sub-divisions and how sub-divisions are the foundation and building blocks of ALL rhythm.
In this post, we will take things a step further and get you learning all of the most important sub-divisions and I’ll show you how to practice them to take your rhythm skills to the next level.