Reps per day. Dan John uses those rules for Easy Strength and goes deeper into the topic in Intervention when he talks about "realistic reps". His opinion is that you can do a certain amount of relatively heavy (-> heavy enough to promote strength adaptions, but still light enough that you can recover overnight) lifts per day***.
- "Rule of 10" (-> 10 reps per day) applies to big, demanding full body lifts. DJs examples in Intervention are deadlifts, snatches and C&Js. Examples for rep schemes would be 2x5, 5x2, 3x3, 10 singles, 5-3-2.
- Next is the "Half Body Movements - 15-25reps", which applies to things like pullups, rows, bench press, press and all that stuff. Note that DJ puts the squat in there, too. The usual rep schemes like 3x5, 5x5, 3x8, 4x6 are examples of this.
- Last are the "Explosive Full Body Movements - 50-100reps". Examples are KB swings or snatches.
S&S is a perfect example of this. 10x10=100reps of swings and "Rule of 10" TGUs every day.
PttP with its 2x5/5-3-2 =10reps would be another.
***Please note that this refers to a single lift. In Easy Strength you use the Rule of 10 for all lifts, because you do 5 lifts per day and not just one.
For example if you'd only do pullups you can easily get away with 15-25 per day, but when you also do DLs, squats, bench and ab-wheel cut down to a max of 10 per lift.
It's all about repeatability.
Please read Intervention to grasp the whole concept, because you'll understand it much better than from just a few sentences here and there on the forum.