Hello! I am reading some stuff about the tracker of a detector in a particle collider and I am not sure I know what stubs are. They appear without any definition: "To be used for the primary vertex finding task, the resulting tracks must have stubs in at least four different tracker layers". I didn't really find a definition online. From this sentence I guess a stub is like an accumulation of energy in certain cells inside a layer of a tracker (those cells form the stub) but I am not totally sure. Can someone clarify this? (I am reading about the CMS detector) Thank you!