What is hoisting in JavaScript?

Hoisting is JavaScript's default behavior of moving variable and function declarations to the top of their containing scope during the compilation phase. This means you can use functions and variables before they are actually declared in the code. However, only the declarations are hoisted, not the initializations. `let` and `const` are hoisted as well, but they are not initialized, leading to a `ReferenceError` if accessed before declaration. 

console.log(hoistedVar); // undefined
var hoistedVar = 'I am hoisted!';

hoistedFunction(); // 'I am hoisted!'
function hoistedFunction() {
  console.log('I am hoisted!');
}

console.log(notHoistedVar); // ReferenceError: notHoistedVar is not defined
let notHoistedVar = 'I am not hoisted!';