Org mode uses ‘#+BEGIN’ … ‘#+END’ blocks for various purposes from
including source code examples (see Literal Examples) to capturing
time logging information (see Clocking Work Time). These blocks can
be folded and unfolded by pressing TAB in the ‘#+BEGIN’
line. You can also get all blocks folded at startup by configuring
the variable org-hide-block-startup or on a per-file basis by using
#+STARTUP: hideblocks #+STARTUP: nohideblocks