a knot at the end of a cord or rope that can slip along the cord or rope around which it is made
"The climber adjusted the loose slipknot on his carabiner before securing his harness."
Alternative spelling of slip knot
"The sailor tied his rope in a slipknot to ensure it could be quickly released if needed."
In plain English: A slipknot is a type of knot where you tie a loop around your finger to make it easier to tighten and secure tightly.
"The old rope began to slip on his hands, so he tied another knot to secure it better."