Cold press Watercolor paper has texture to its surface or tooth. They both mean the same thing, little bumps and grooves allow for texture and creative techniques. This paper is sometimes referred to as "Not" which simply mean not hot pressed. Cold pressed "Not" and Rough are the most popular papers with watercolour artists
Hot press in comparison is very smooth, and allows for detailed and vibrant paintings.
Quality watercolour papers, allow your paints to have more vibrancy.