Help - Glossary -
H - Halo
Every Morph on the screen has a halo around its boundary when
Cmd Left Clicked (or with the middle mouse button, if you use a 3 button mouse). The
halos are in fact a number of icons that when clicked give access to some of
the things any Morph can do and often some of the things the Morph one clicked
on can do.

If you put the cursor on a halo (not in the above gif-picture, but on any morph in Squeak) you will get a balloonhelp that tells you what it does. Try it with Cmd-d, for example on
StarMorph new openInWorld
which pops up a small blue star in the upper left part of the screen. Play with this to see what you can do!