TDMA multiplexing systems divide a radio frequency into time slots which are allocated for multiple data streams, for example cellular phone calls. This means that a short piece of data from each stream is inserted after each other, this way a single frequency can support multiple simultaneous channels. In GSM networks one time slot burst is usually 156.25 bits long. 8 separate time slots are used, they form a TDMA frame which is transmitted every 4.615 ms.
Here is a diagram which shows the use of a frequency and the way it is split into 8 individual time slots:
--->
time
_________________________________________
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 1 | 2 | ...
|___|___|___|___|___|___|___|___|___|___|
|---|
slot
|-------------------------------|
frame
Sources of information:
A Brief Overview of GSM by John Scourias
Radio Transmission in GSM, http://www.handytel.com/