An idiom is defined as - a group of words in a fixed order that has a particular meaning that is different from the meanings of each word on its own.
let out a rope
to allow a rope to slip out little by little
We let out the rope as the boat left the shore.
List of common idioms, their meanings and examples of their usage in sentences
Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.