Operators are methods that you can use on Observables/Subjects that allow you to change the original observable and return a new observable. Operators do not change the existing Observable, they simply modify it and return a new observable. Operators are known as pure functions, which are functions that do not modify the variables outside of its scope.
Operatoes are of two types:
Static operators are usually used to create observables. You will find these mainly under the creation operators.
Instance operators are methods on observable instances. Majority of RxJS operators that are used.