what does the term washing mean? thanks

Washing is a technique where you use diluted paint
enamel-turpentine or acrylic-water and paint that more or less on your model. because it`s diluted it will go into the deeper parts of your model to leave there a shady layer.
I use it mostly if I want to get deeper parts to appear darker.

do a search aroud on the forum of this site this has been passed by a million times you probably get to know more about this washing technique

my two cents

Primary purpose of a wash is to create depth and shadow to the model. Its usually done with a dark colour (normally of the base color) using oil/diluted enamel paints. Ive heard some folks on this site who uses acrylics as well.......