A door slammed shut is one that has shut on the latch alone, without the key being turned, usually when going out in a hurry, in a draught or when taking the rubbish out. It cannot be opened from outside without a key, but the lock is not jammed.
It is the most common incident and also one of the simplest to sort out: as the deadbolt is not thrown, most doors can be opened without breaking anything and the lock can still be used.
If it happens to you, do not try to force it with a card or a screwdriver, because you may damage the frame or the lock. Message us on WhatsApp with a photo of the door. Before opening we will check that you have the right to go in. More under door slammed shut.