How do you define a function in JavaScript?

Defining a function in JavaScript is done using the keyword 'function', followed by a name and parentheses. This syntax is fundamental to JavaScript and allows for the creation of reusable blocks of code. When you use 'function', you initiate the definition of what constitutes a function, which can then be called or invoked later in the code.

The parentheses are crucial as they can include parameters, allowing values to be passed into the function when it's called. This structure enables developers to encapsulate logic within a function, making code modular and easier to maintain. The function name acts as an identifier, allowing the function to be referenced and executed throughout the codebase. Overall, this approach to defining functions plays a key role in JavaScript programming.