Gouache is a type of paint, and its main appeal is that it is water-based, similar to watercolour with an opaque characteristic appeal. Other than that, it is very similar to acrylics. However, the fact that it's water-based renders it different uses than acrylics. It could also be described as concentrated watercolours, which makes it heavier and more opaque. Similar to watercolour you can rewet your paint in the palette and use the paint for your next painting project.