Here's the elementary school version...
This is usually trained for with higher volume and the goal is to increase the energy stored withing the muscle. This creates a swelling of the muscle making it larger. This type of hypertrophy is the easiest lost when training is diminished. Some numbers indicate that it will be responsible for ~20% of overall potential.
This type of hypertrophy is usually trained for with heavier weights and fewer reps. This type of hypertrophy makes the actual muscle tissue larger. It will remain longer when training is decreased. Some numbers indicate that it will be responsible for ~80% of overall potential.
Feel free to add more college level talk to this