What is the difference in a watercolor wash and an acrylic wash?

Answer 1

The concept is the same and even the result, in most cases, will look the same. You can however make different effects with both because of the way the paint 'behaves' when dry .

A watercolor wash will always stay susceptible to water. Doing a second wash can, if you want, change the first coat.

An acrylic wash, when dry, will never change again.

Answer 2

There's no difference, both are washes, meaning a transparent diluted coat on a surface. Just that one is watercolor and the other is acrylic.