Obstruction, as in a pipe, is a term used to describe an object that is blocking the flow of something. In this case, it is referring to a BLOCKAGE in a pipe, which can be caused by a variety of things such as debris, corrosion, or a foreign object. This can cause a disruption in the flow of whatever is passing through the pipe, and can lead to further problems if not addressed. The 8-letter crossword solution for this term is 'BLOCKAGE'.