How the common splits divide the week
Training splits organize which muscles are trained on which days. A bro split dedicates each day to one or two muscle groups, training each roughly once a week. Push-pull-legs groups movements by function and often hits each muscle once or twice. Upper-lower alternates the body in halves, while full-body trains everything each session.
Each arrangement is really a different way of distributing the same weekly volume across sessions.
Frequency versus volume per session
The main tradeoff is frequency against per-session volume. Splits that train a muscle more often spread sets into smaller, fresher doses, which research on equated volume tends to favor slightly or rate as equivalent. One-day-per-muscle splits concentrate volume but train each muscle less frequently.
Because total weekly volume appears to be the dominant driver, the best split is often the one a person can train consistently and recover from. This is general educational information about program structure, not individualized coaching advice.