Cognitive load
Also said as Mental load, Working memory limit, Too much at once
How much a person has to hold in mind at once. John Sweller developed cognitive load theory in 1988, from research on how people learn.
Attention is limited, and the limit is smaller than designers think. Cowan argued in 2001 that people hold about four chunks at a time. Everything on your screen and in your tutorial uses some of that. Load itself is hard to measure, and researchers argue about how to do it, but the limit is easy to feel.
Say it
“The tutorial asks them to learn movement, crafting and the map in one screen. Split it: walking only in room one, crafting only after the first enemy, map when they first get lost.”
Where you’ve seen it
Portal teaches one new idea per room, each tested alone before it is combined with others. By the end you are managing several at once without ever having been overloaded.
Not to be confused with difficulty
Difficulty is how hard the challenge is. Load is how much you must keep track of to engage with it. A chess puzzle is hard with little to track; a cluttered menu is easy but heavy.