What is the difference between a static variable and a regular variable in programming?

A static variable differs from a regular variable in that it retains its value between function calls or throughout the entire runtime of the program, whereas a regular variable is recreated each time and destroyed after exiting its scope.

For example, in Swift, a static variable inside a class or structure belongs to the type itself, not to an instance, and exists as a single instance:

class Counter {
    static var totalCount = 0
    var count = 0

    func increment() {
        count += 1
        Counter.totalCount += 1
    }
}

let a = Counter()
a.increment()
print(a.count) // 1
print(Counter.totalCount) // 1

let b = Counter()
b.increment()
print(b.count) // 1
print(Counter.totalCount) // 2

Here, count is a regular instance variable, and totalCount is a static variable shared among all instances of the class.