Disclaimer: not a string theorist. In examining the behavior of superstrings, we are concerned with modes of oscillation. As with ordinary strings, the possibl

Disclaimer: not a string theorist. In examining the behavior of superstrings, we are concerned with modes of oscillation. As with ordinary strings, the possible oscillations are determined by the boundary conditions on the string. E.g., both ends of the string can be fixed; both ends can be variable; one end can be fixed, one variable. One dimensional strings in a three dimensional space really just have a couple of possible conditions. Superstrings oscillate through as many as 10 dimensions. That means there are many more possible boundary conditions. They come in groups. As an analogy, if a dimension ranges from 0.0 to 1.0, the string behaves pretty much the same regardless of whether its end is fixed at 0.5 or 0.6. What matters is that it is fixed. We can group the "fixed endpoint" conditions together. The collection of boundary conditions on a superstring defines a "sector". The "hidden sectors" is the part I'm less clear on. I think that refers to the many combinations of boundary conditions that would produce a string theory that we simply can't observe. I.e., all the strings we see as bosons, fermions, charge carriers, etc. share some sector. But the underlying math allows other string theories to exist. They are internally consistent but would result in particles we could not observe. And, of course, 100% of this is based on string theory which is, thus far, unproven.