Below is a list of some useful terms we use with regard to Atom.
A buffer is the text content of a file in Atom. It's basically the same as a file for most descriptions, but it's the version Atom has in memory. For instance, you can change the text of a buffer and it isn't written to its associated file until you save it.
A command is a bit of functionality in Atom that can be triggered by the user either through a keybinding or a menu item.
A key combination is some combination or sequence of keys that are pressed to perform a task.
A key sequence is a special case of a key combination. It is a key combination that consists of keys that must be pressed and released in sequence. Ctrl+K Down is a key sequence. Alt+S is not a key sequence because it is two keys that are pressed and released together rather than in succession.
A keybinding is the mapping of a key combination, such as Ctrl+Enter to an Atom command.
A keymap is a collection of keybindings. It can also refer to a file or files containing keybindings for an Atom package or Atom itself.
An Atom plugin. There is a bunch more information in the section on Atom Packages.
A pane is a visual section of the editor space. Each pane can hold multiple pane items. There is always at least one pane in each Atom window.
Some item, often an editor, that is displayed within a pane. In the default configuration of Atom, pane items are represented by tabs at the top of each pane.
Note: The reason why we don't call them "tabs" is because you can disable the tabs package and then there aren't any tabs. For a similar reason, we don't call them files because some things can be shown in a pane that aren't files, like the Settings View.
A piece of the Atom UI that is outside the editor space.