Compact dimensions
There are an infinite number of ways to wind a string around an extra dimension. Each way is topologically described by an integer called the winding number, which can be positive or negative depending on the orientation of the string. The wound string is stretched along the compact direction, but from the point of view of ordinary 3D space it is located at a point and therefore looks like a particle. The winding number is simply a new kind of quantum number. String theory therefore has lots of possibilities for describing the complicated conservation laws and internal symmetries of elementary particles.