What is a p = 1 brane and a p = 2 brane?

P-branes have directional lengths and are best used in relation to supersymmetry at the 10th or 11th dimensions. A p = 1 brane is a string and a p = 2 brane is a surface. However, p = 1 branes are no longer considered the best to use when discussing the smaller dimensions of 1 or 2.