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.