Which statement is true about JavaScript's 'var' keyword?

The statement about JavaScript's 'var' keyword being associated with hoisting is accurate. When you declare a variable with 'var', the declaration is processed at the top of the function or the global scope regardless of where it appears in the code. This means that you can reference a 'var' variable before its actual declaration line in the code, and JavaScript will treat it as if it has been declared at the top of the scope.

For example, if you have a 'var' variable declared inside a function, you can access it even before the line where the variable is defined, which may lead to undefined behavior if you're expecting it to have a certain value. This behavior differs significantly from variables declared with 'let' and 'const', which do not allow access before their initialization due to block scoping.

The other statements do not accurately represent the characteristics of 'var': it can indeed declare variables within functions, does not support block scope (that's 'let' and 'const'), and it does not define constants. Therefore, the focus on hoisting is a key feature of the 'var' keyword that highlights its unique behavior in JavaScript.