explicit-locking.html "key values" reference

hi.
https://www.postgresql.org/docs/current/explicit-locking.html

FOR KEY SHARE
> Behaves similarly to FOR SHARE, except that the lock is weaker: SELECT
> FOR UPDATE is blocked, but not SELECT FOR NO KEY UPDATE. A key-shared
> lock blocks other transactions from performing DELETE or any UPDATE that
> changes the key values, but not other UPDATE, and neither does it prevent SELECT
> FOR NO KEY UPDATE, SELECT FOR SHARE, or SELECT FOR KEY SHARE.

A key-shared lock blocks other transactions from performing DELETE or any
> UPDATE that changes the key values

querya: select col1,col2,col3 from a for key share of a
Does "the key values" refer to these rows returned by the querya?
I still feel confused about "the key values".