Org is an outliner. Outlines allow a document to be organized in
a hierarchical structure, which, least for me, is the best
representation of notes and thoughts. An overview of this structure
is achieved by folding, i.e., hiding large parts of the document to
show only the general document structure and the parts currently being
worked on. Org greatly simplifies the use of outlines by compressing
the entire show and hide functionalities into a single command,
org-cycle, which is bound to the TAB key.