What does it mean for a dog to knot?

It means that the dogs penis grows inside ur vagina until it cannot be removed. It helps bette the chances of a succesful mating. If it happens it will go down in abput 20-45 minutes.
part of a dogs penis located right after the testicles but before the penis. it is meant to lock the penis in the vagina of a female dog until all sperm is delivered.
a dogs knot is a swelling near the base of a penis of a dog which holds hm into the female to stop any leakage of sperm to ensure the female gets the highest chance of being pregnant