Web development covers building and running the software behind a website or web application — the pages a visitor sees, the systems underneath them, and the work of keeping both online afterwards. In practice the label spans very different jobs: a brochure site on a content management system, a customer portal wired into an existing back office, and a full product delivered as a web application are all sold as web development.
The questions that separate providers are less about language and more about scope. Does the engagement end at launch, or does it include hosting, monitoring and updates? Who owns the code and the repository afterwards? Is the work fixed-price against a specification or time-and-materials against a backlog? A team that builds well but hands over nothing maintainable costs more in the second year than it saved in the first.