settling the shape
Settling the shape is the opposite of keeping flexibility. aji-keshi and kikashi are two flavours of settling the shape.
Mostly a player will settle the shape when he sees a sequence giving him undisputed victory or a definite advantage. Settling the shape may also be a good strategy if you want to eliminate your opponent's forcing moves or ko threats before playing elsewhere. Some players will also do it as a matter of style, perhaps because they are less at ease when their opponent has a lot of choices. Kobayashi Koichi is said to be such a player. To many people, settling the shape early is against the true spirit of the game.
In Killer of Go, Sakata comments a game of his against Go Seigen, in which he didn't know how to handle a certain area. "So I settled the shape first and then decided how to play."