Headlines define the structure of an outline tree. The headlines in Org start with one or more stars, on the left margin4 5. For example:
* Top level headline ** Second level *** 3rd level some text *** 3rd level more text * Another top level headline
Some people find the many stars too noisy and would prefer an outline that has whitespace followed by a single star as headline starters. Clean view, describes a setup to realize this.
An empty line after the end of a subtree is considered part of it and
will be hidden when the subtree is folded. However, if you leave at
least two empty lines, one empty line will remain visible after folding
the subtree, in order to structure the collapsed view. See the
org-cycle-separator-lines to modify this behavior.