Mixing liquid ingredients to "just combine" to dry ingredients for muffins
As Adele suggested in the comments, this is a common instruction to guard against overmixing. You mix everything in, and mix it until it's just barely combined. You just want to make sure there aren't any big pockets of dry ingredients; once all the wet and dry is combined, you're done.

If you're curious why you don't want to overmix, see a previous question: Over-stirring muffin mixtures.