Washing is mainly about shading, but I'd say that you can also use it to pick out and edge detail (like putting a wash over the pommel of a sword to edge the gem but not affect the colour too much).
Shading as a phrase is just making the shadowy/recessed bits darker, but as a technique then it is more likely to be the inverse of highlighting (taking a darker shade and painting it into the recesses by hand - mainly used on cloaks).
As Snowblizz said then their are different ways of highlighting, like drybrushing. Drybrushing is about using the existing texture (particularly fur, hair and chainmail armour) to pick out your highlights by removing most of the paint from your brush on a tissue and letting it collect on the highest points as you brush across the texture. Just make sure you use a proper drybrush as it'll kill a normal brush quite quickly.
As an aside, didn't they have a wash before and then rename it to an ink? I seem to remember it was the wash and the glaze. Washes (like black/red/blue/yellow/brown/chestnut/armour) had blue lids and glazes (in blue/red/purple and others that I can't remember) had red lids. They then dropped the glazes and just had inks, which could be watered down to act like a glaze (I think) and now they seem to have renamed it all to "wash". At least that's what I remember.
Also, that adds another (possibly now outdated) phrase: glazing. Basically, if you highlight and it ends up to pale or chalky then you can use a thinned wash (formerly a glaze) to just tint the colour back to something more reasonable without causing it to pool in the recesses.
Hope that helps