Web Development broadly refers to the tasks associated with developing functional websites and applications for the Internet. The web development process includes web design, web content development, client-side/server-side scripting and network security configuration, among other tasks.
HTML, aka HyperText Markup Language, is the dominant markup language for creating websites and anything that can be viewed in a web browser.
HTTP, aka HyperText Transfer Protocol, is the underlying protocol used by the World Wide Web and this protocol defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.
CORS, aka Cross-Origin Resource Sharing, is a mechanism that enables many resources (e.g. images, stylesheets, scripts, fonts) on a web page to be requested from another domain outside the domain from which the resource originated.