A file containing the actual content of an item or a layout. Usually, there will also be a meta-file containing metadata about that item or layout, although some data sources (e.g. filesystem) merge the content file and the meta-file into a single file.
An object that reads data from a given location and turns this data into items and/or layouts. By default, data can be read from the filesystem, but data sources for databases and online web services are also possible.
An object that transforms content from one format into another format. There are filters that evaluate embedded Ruby code (erb, haml), filters that transform from text to HTML (bluecloth, redcloth), filters that “clean” HTML (rubypants), and more.
A module that, when included, offers additional functionality such as easy linking to pages, building XML site maps or Atom web feeds.
A "version" of an item. For example, an item can have an HTML, an XHTML, a JSON and a YAML representation. A single representation corresponds to one output file (or zero, if the representation does not have a path).