The word clog has two main meanings:

1. A type of shoe with a thick, sturdy sole, traditionally made of wood. Dutch clogs are famous examples, carved entirely from wood and worn by farmers for centuries because they protected feet in muddy fields and barns. Modern clogs often have wooden soles with leather or fabric tops. They make a distinctive clomping sound when you walk.
2. To block or become blocked so that things can't flow through properly. When hair clogs a drain, water backs up in the sink. Leaves might clog rain gutters, causing water to overflow. You can also use the word to describe traffic: cars clog the highway during rush hour, barely moving.

The verb form connects to the noun: imagine trying to run in heavy wooden shoes. They'd slow you down and make movement difficult, just like a clogged drain slows down water. When something gets clogged, it's stuck and sluggish, unable to work the way it should.