Last TechThursday we explained the different types of vias. Vias are one of the three types of holes we have on the PCB. The other two are through holes without metallisation (NPTH) or with metallisation (PTH), a copper coating called a copper sleeve.
This TechThursday video explains why there are unavoidable manufacturing tolerances in all three types of holes and why these tolerances need to be considered in PCB design.