There are two kinds of scope in JavaScript, global and local. Global scope refers to varaibles that are defined outside of a function and can be accessed and modified from anywhere. Whereas local variables are defined withtin a function and can only be accessed within the function.
Think of it like a locked house. The variable inside the locked house (function) has a local scope and cannot be accesed from outside, however a variable outside the house (function) can be accessed from anywhere because it is not bound by the same restrictions as the variable with a local scope.