What is the purpose of the 'let' keyword in JavaScript?

The 'let' keyword in JavaScript is utilized to declare variables that are block-scoped. This means that any variable defined with 'let' is only accessible within the nearest enclosing block, such as within a pair of curly braces, a function, or a loop. This scoping behavior contrasts with the traditional 'var' keyword, which defines variables with function scope, making them accessible throughout the function in which they're defined. By using 'let', developers can avoid issues related to variable hoisting and conflicts within nested blocks, thereby enhancing code modularity and readability.

The other options do not accurately describe the purpose of the 'let' keyword. For instance, using 'let' does not create global variables, nor does it create constant variables (that would be the role of 'const'). Additionally, while you can use 'let' inside functions, it does not pertain to denoting function expressions. Understanding the block-scoping nature of 'let' is key to leveraging it effectively in modern JavaScript programming.