String of pearls
Also said as Rivers and lakes, Beads on a string
A fixed sequence of open areas. Inside each pearl you can roam and do things in any order. The string between them is the plot, always in the same order.
It gives the player freedom where it is cheap and keeps control where the story needs it. The writer knows what has happened at each beat of the plot, every time.
Say it
“Build the story as a string of pearls: five explorable zones, in a fixed order, with the plot only advancing at the door between zones. Side content stays inside its zone.”
Where you’ve seen it
BioShock moves you through Rapture one district at a time in a fixed order, and within each district you can go back and forth to search and scavenge before moving on.
Not to be confused with linear
A corridor gives you no room to wander at all. A string of pearls is just as fixed in its order, but with room inside each stop.