Synthetics or robots are a type of people. They're typically made of metal, as you would expect, but some take more esoteric forms such as programs or operating systems. Even those that have an obvious physical form are not always humanoid in shape. They range in their ability to vary from their initial programming.
Mechs are technically synthetics, though the majority are not conscious. Divines are usually considered a unique form of life distinct from other synthetic beings, but this distinction a matter of popular perception, and doesn't reflect an inherent difference between the two groups.
Stel Columnar is a society of synthetics.