What is Shellack?

Shellack definition and meaning on Dictionary terms:

lac that has been purified and formed into thin sheets, used for making varnish.
a varnish (shellac varnish) made by dissolving this material in alcohol or a similar solvent.
a phonograph record made of a breakable material containing shellac, especially one to be played at 78 r.p.m.: an LP that can hold nearly 10 times as much as the old shellac.