Not saying everyone should train like this but for the longest time I generally train three days a week. I use the split of back and chest on say Monday. Wednesday is legs. Friday is delt and arms. Weekends are off. Some argue a body part should be trained more than once a week but there is so much overlap. Such as bicep and tricep gets hit hard on back and chest day. No way to avoid it with the pulling and pushing. Chest gets hit again on friday with dips and close grips for tricep. Back gets hit again with such things as squats and clean for military presses. Legs get a direct day and get hit again on back day with deadlifts or cleans. In reality body parts are getting hit twice a week.
On the four days off can be rest or cardio.