Recall methods. A method is some piece of code that can be “called on objects”. There are two things to methods: They’re meaningful with an object to call on, and their interface looks like “they can be called with some arguments to return a value”.
Properties are similar to methods, in that a property is meaningful when paired with an object. They have a different interface than methods, though: you don’t “call” them; instead you “get” and “set” their “current value”.
We normally consider properties and methods to be some abstract “traits” of objects. But why not treat them as first-class objects too? Imagine properties and methods as building blocks for object interfaces. A method would be an object that describes callable parts of other objects, while a property describes readable and assignable parts.