RSS (Really Simple Syndication) is a web feed format that is used to publish frequently updated content, like news articles, blog posts, etc. It is a format that is particularly suited to being read by computers, and is therefore the preferred way of getting content from the web into an e-book. There are many other feed formats in use on the Internet, and calibre understands most of them. In particular, it has good support for the ATOM format, which is commonly used for blogs.
A recipe is a set of instructions that teach calibre how to convert an online news source, such as a magazine or a blog, into an e-book. A recipe is essentially Python code. As such, it is capable of converting arbitrarily complex news sources into e-books. At the simplest level, it is just a set of variables, such as URLs, that give calibre enough information to go out onto the Internet and download the news.
HTML (Hyper Text Mark-Up Language), a subset of Standard Generalized Mark-Up Language (SGML) for electronic publishing, is the specific standard used for the World Wide Web.
CSS (Cascading Style Sheets) is a language used to describe how an HTML document should be rendered (visual styling).
API (Application Programming Interface) is a source code interface that a library provides to support requests for services to be made of it by computer programs.
LRF The e-book format that is read by the SONY e-book readers.
URL (Uniform Resource Locator) for example:
Regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters. See the tutorial for an introduction to regular expressions.