The part or percentage of a
liquid that remains stuck on the inside of a: container,
bottle, plastic bag,
cup that you can't get out without destroying what you are after.
It's impossible to get all the ketchup out of a ketchup bottle, there is always some stickage left there at the end, so you
never get the full amount. The same with tomato
sauce in jars, and liquid medicine - some always sticks to the
bottom and sides.