Sorry, not correct. A demurrer tests the sufficiency of a pleading. The motion to dismiss asserts that even if a cause of action is asserted properly, there is no claim.
So for example, a demurrer to a breach of contract claim may say that the person did not plead damages because a breach of contract claim requires contract, breach and damages. That is why the court looks at almost like mistake and gives the pleader 2 or 3 shots at correcting.
A motion to dismiss says all the elements are there but the trier of fact will never see damages. So if you sign a contract to buy a house and you pay nothing including no down payment and the seller breaches and you buy another house, you probably don’t have a breach of contract claim because you didn’t pay anything and there were no damages. Or the trier of fact would never conclude that you had a real contract and therefore, the court will dismiss.
And a demurrer is a type of motion. Any filing that asks the court to rule or act is a motion or a type of motion.