Texture Paste is primarily used as a artists painting medium to give artists paint a greater body, thickness and texture. It's similar to texture gel however it often reduces the original viscosity of the paint.  

Texture paste can also be used by artists to create an underlying texture, or embossed effect, aside from painting, some people use it in paper crafts such as scrapbooking as an embossing medium.

Texture Paste is commonly made from a binding agent, normally an acrylic base and an additive such as marble dust. There are many types of pre-prepared texture pastes available with various additives such as marble dust, crushed glass, sand, refined silica, mica, frit and more.

A good texture paste will hold its shape and the finest peaks created by the brush or palette knife once it is dry. These qualities are generally the most sort after by painters who like using texture pastes when creating impasto paintings.

Artistically speaking you can use almost any paste like substance as a texture paste, as an artist you are free to experiment! 

Also see: Texture Gel or Painting Mediums. You can buy Texture Gels from any Art Supplies Store or Sculpture Supplies Store.