Frequency analysis is done in discrete space (as with anything done with a signal on a computer), usually involving the FFT. The FFT is defined by a number of points (e.g. 1024) which gives that many discrete frequencies at which results are given.
I don't like the term 'bins' myself when I am working with frequency in this context so the exact meaning would depend on the context in which you are seeing it.
Some people may refer to these discretised frequency points as being bin centres, with the "bin" spanning half way to the previous and next points.
e.g. if you have frequency points defined at 1 Hz intervals these may be considered as bin centres, the bins being e.g. 0.5-1.5, 1.5-2.5, etc.
As I said, personally this is not terminology I use because I consider it misleading and I don't know where your "many places" are to understand exactly what their context is.
