The LNB stands for "Low Noise Block". or "Low noise block downconverter".
It takes the satellite signal, amplifies it, and downconverts it to a lower frequency signal easily carried by coaxial cable.
Back then, it was called an LNA or "Low Noise Amplifier" and the down conversion was done on the receiver's end. It used a fat cable to carry the 3-4 ghz signal.
Later systems used a downconverter mounted outside near the dish, and used plain ol RG-6 to carry the signal to the receiver.
Then once electronics could be packed into a smaller area, the LNB came out.