From my understanding they are 'usually' one and the same but not always. Twist weld refers to the method of forming a barrel from a strip of steel which may or may not be damascus steel showing the distinctive pattern associated with steel fashioned by the damascus method. Some barrels were twist welded with normal steel which would only show the twist pattern from the welded joints. It was not unheard of for some normal steel twist barrels to be given a fake damascus pattern to raise the value of the firearm.