There are a number of different versions
of the Terminator.
The original Terminators created by skynet had rubber skin and were very easy to detect and destroy.
Later the T-800 was created. This terminator was often adorned with human skin. This made them much more difficult to detect. Dogs were often used for this purpose. The kind of Terminator that was originally sent to kill Sarah Connor was a T-800. It was also the kind that was reprogrammed and sent back to help save Sarah and her son later.
After this the T-1000 was developed. This kind of terminator was created out of liquid metal which allowed it to change its form into anything that it touched. This adds both resiliance and stealth to the machine. The-T 1000 was the type of terminator sent to kill Sarah's son.
Somehow these machines managed to find themselves in two movies of the same name.
Along with the various androids, a terminator is one who terminates.
It is also a device that ends electrical signals.