A training split is how you divide your muscle groups across the training days of a week. It determines what you train when and how often each muscle gets worked.
The three common options
Full body on three days: every muscle is trained three times a week with a few compound lifts that are easy to progress. A good fit for beginners, people returning after a break and anyone short on time.
Upper and lower body on four days: every muscle is worked twice a week, with more volume per session. A good middle ground for most people once full-body sessions get too long.
Push, pull, legs on six days: push covers chest, shoulders and triceps, pull covers back and biceps, plus a leg day, each twice a week. It takes a lot of time and good recovery and is not the best choice for beginners.
What matters more than the split
A meta-analysis by Schoenfeld, Ogborn and Krieger (2016) found that training each muscle twice a week produced more growth than once a week. A newer, larger analysis (Pelland et al. 2026) found only a possibly negligible effect of frequency when volume was equal. So weekly volume per muscle is what counts most.
Example: Whether you spread 12 sets of chest across two or three sessions is mostly a practical question: how many sets can you do in one session before quality suffers? This is an example.
So pick the split that fits your week and that you can stick with for months.