Web development refers in general to the tasks associated with developing websites for hosting via intranet or internet. The web development process includes web design, web content development, client-side/server-side scripting and network security configuration, among other tasks.
In a broader sense, web development encompasses all the actions, updates, and operations required to build, maintain and manage a website to ensure its performance, user experience, and speed are optimal.
It might also, but not necessarily, include all those strategic actions needed to ensure its proper ranking on search engine results. Usually, those tasks pertain to a different specialization, namely search engine optimization (SEO)
Web development is also known as website development, while the professionals that maintain a website are called web developers or (more commonly) web devs.