A training split alternating upper-body and lower-body sessions, usually four days a week, giving each half two sessions.
The standard week is upper, lower, rest, upper, lower, with the weekend off. Each muscle gets trained twice, which is where most of the evidence on frequency sits, and each session is short enough to finish in an hour.
It is the best default for a client who can train four days a week. Two upper sessions give room for a horizontal press, a vertical press, a horizontal pull and a vertical pull across the week without any single session running to 90 minutes.
A worked upper day: bench 4 x 6, row 4 x 8, overhead press 3 x 8, lat pulldown 3 x 10, then two arm exercises. The lower day: squat 4 x 5, Romanian deadlift 3 x 8, leg press 3 x 10, leg curl 3 x 12, calves.