This is the 7950th most frequent Japanese word.
外せる
"外せる" means "can be removed" or "detachable."
In this sentence, '外せる' means 'can be removed', indicating the belt has a feature allowing it to be taken off.
この時計のベルトは外せるタイプです。
The belt of this watch is removable.
Here, '外せる' is used to mean 'can be excluded or left out', showing the importance of the person in the context.
彼はこの試合で決して外せる選手ではない。
He is definitely not a player who can be excluded from this match.
In this example, '外せる' implies 'can unlock or detach the key mechanism', talking about the lock's functionality.