Browser: We all know what it is.
Rendering Engine: A part of the browser which converts the HTML code accessed from the server to a human-readable/ presentable form.
HTML: HyperText Markup Language, a markup language used for writing web applications, it is used for providing the structure to a web page.
CSS: Cascading Style Sheet, another language used for styling the HTML structure of the web page.
JavaScript: A scripting language, used for providing behavior to a web page. JS is mostly used at the client-side of web applications, however, it can also be used at the server-side.
DOM: Document Object Model, represents a document in the form of nodes and objects. It provides a way to define and interact with the web page (a document), including altering/ changing the structure, content, and style of the page.
Developer Tools: All popular browsers include a set of developer's tools, these tools provide a way to interact with HTML, CSS & JS of a web page at the runtime. Additionally, developer's tools provide more functionalities such as the flow of requests, access to stored cookies, resource utilization, etc. Visit the link to learn more about developer tools.
Asynchronous requests: In a program, while a call is made to an external resource/ library and a response is awaited, the program however continues with the execution of further statements (or blocks) then these requests are called as asynchronous requests.
AJAX: Asynchronous JavaScript and XML, is a set of techniques used by web applications to send & fetch just the updated data to & from servers. The structure of the web page usually remains the same, only the updated data is fetched from the serve which may bring changes in a section of the page. Imagine a scoreboard application, just the scores are updated leaving the rest of the web page the same.
Web Sockets: An application layer protocol, duplex in nature. Unlike HTTP where only the client initiates communication, here the server may as well start one. Used for real-time applications where the data keeps on changing in real-time, Chat-bots, Gaming apps, etc.