A value that can be changed while a program is running. It's called a variable because it can vary.
Sometimes the term "variable" refers to variables and constants collectively, but while variables and constants are similar, they have one important difference — the value of a constant cannot be changed while a program is running.
Basic syntax for a variable is var name : type = value. The varis a keyword that says this is a variable, and name is a name you assign to the variable (known as the identifier). The : says that a type is coming. The = says a value is coming, then the value itself. For example:
PlayerSpeed : float = 2.0
This says that PlayerSpeed has a value of 2.0, represented as a decimal value that does not change while the program is running.
The name and type is the declaration, and the initialization is where that value is expressed. A variable does not have to have an assigned value when initialized, but it's good practice to do so.
Variables differ from constants in that you can change the value of a variable at any time. This is done with an assignment expression.