Data of a loaded file and additional metadata, associated with one or more views. The distinction between buffer and view is technical. Most of the time, both terms can be used interchangeably.
Graphical display of a buffer. Multiple views can show the same buffer.
A feature implemented in Python, which can consist of a single command or multiple commands. It can be contained in one .py file or many .py files.
This term is ambiguous in the context of Sublime Text, because it can refer to a Python package (unlikely), a folder inside Packages or a .sublime-package file. Most of the time, it means a folder inside Packages containing resources that belong together, which build a new feature or provide support for a programming or markup language.
An input/output widget, such as a search panel or the output panel.
An input widget of a special kind. For example, Goto Anything is an overlay.
file type

In the context of Sublime Text, file type refers to the type of file as determined by the applicable .tmLanguage syntax definition.

However, this is an ambiguous term, and in some instances it could also be used with the broader meaning it has in technical texts.