Is receptor antagonism just long-term binding?
The details of activation vary by receptor of course, but talking in the popular key-lock picture:


An agonist is a key, that fits the lock and opens ("activates") it.
An antagonist is a key that you can put into the keyhole, but it does not open the lock. What this means is: while the "wrong" key is in the keyhole, you won't be able to open the door, even if you have the correct key, as long as the wrong key is in the keyhole.


As far as Wikipedia goes, the articles for Agonist (and the links contained therein) might be more informative than the one you quoted.

https://en.wikipedia.org/wiki/Agonist