A property, which we also commonly call a member variable, is a variable attached to and stored in an object, an entity that groups data (variables) and functions.In Godot, nodes have many properties. Let's take the Sprite2D node for example:
Its texture property stores the image displayed by the sprite.
Its position property stores the position of the sprite in the game world.
Its visible property stores whether the sprite is visible or not.
In a script file, in GDScript, whenever you define a variable outside of functions, it is a property (you can also call it a member variable). For example, this script adds a health property to any 2D node it's attached to:
extendsNode2Dvar health :=100
The technical difference between property and member variable
Properties and member variables are closely-related programming concepts: They're both variables attached to an object, and we often use these terms interchangeably.The nuance between them is that a property builds upon a member variable and reads and writes data through an extra mechanism, typically a getter and a setter function. In Godot, when you define a member variable, under the hood, Godot reads and writes to it through a getter and a setter function. So technically, all member variables in Godot are properties.