Difference between a closed door and a locked door?

A lot of times when I put my dogs in their kennels I don’t latch the door, just close it. Sometimes, the dogs act like the door is locked anyway… Sometimes they push their nose on it, swing it open, and walk out.
Sometimes I’ll stand in front of an unlocked but closed door, and wait for someone else to come up too, just to see if they try to open it, or assume since I’m there it’s locked…

I was just wondering… what do you think is the difference between a closed door and a locked door? Do they have the same effect?... Or no?
And, what different ‘doors’ have you run into in life—how did you handle them? Were they locked, or just closed? How did you find out?

(Recently I’ve realized that a door I’ve been staring at for a very long time thinking was locked, wasn’t… I could have always gone through it, if I just tried…)