"Synthetic" is the politically correct term for an artificially intelligent computer. An artificial intelligence (AI) is capable of learning and independent decision making--capabilities beyond the simple virtual intelligence (VI) software used as computer operating systems.
An AI requires both quantum computing hardware (brain) and adaptive software (consciousness). When first brought online, an AI runs at a very low processing speed, with a handful of input sources, and the intellectual capability as a newborn human. AIs experience life at the speed their hardware runs, and can absorb information from millions of sources at once. If "switched on" at full capacity, they cope badly with the deluge of input. At best, such an AI is severely autistic; at worst, it is insane.
As operators teach AI to reason and filter incoming data, they increase the AI's processing speed. At a year's age, an AI can observe, consider, and react hundreds of times faster than its organic creators. Mature AIs may be frustrated by the comparative "slowness" of the organics they must interact with.
Galactic culture mistrusts synthetic life. While physically immobile, an AI can assert its will by taking control of networked computing systems. AI laboratories are physically isolated from the galactic extranet and placed in remote, uninhabited locales.
Some futurists believe the ascendancy of synthetics is inevitable. The theory of technological singularity asserts that as the rate of technological advancement increases, there will come a point at which AIs can modify themselves faster than organics can. Eventually, synthetic life will be able to self-evolve so rapidly, organics will lose the ability to comprehend the process.
Not all believe such an evolution to be negative. Transcendency cults believe organic minds will one day be uploaded and emulated as software data, providing synthetic immortality.