A robot was a machine designed with enough intelligence to replicate human behaviors and characteristics.
From as early as the mid 20th century, one individual named Ted Buchanan created a robotic duplicate of himself that was able to maintain itself for over forty years, following a murderous cycle without suspicion until he was destroyed in 1998 by Buffy Summers.
A year before that, Buffy encountered a demon that placed his consciousness into a large, robotic body before being defeated.
In the early 21st century, tech student Warren Mears built robot duplicates of himself and Buffy (dubbed the "Buffybot") along with a robotic girlfriend of his own, named April. Both the Buffybot and April lacked the tactful skills of Ted's robot and were also dependent on a human proprietor to look after them. They were, though, programmed with superior fighting skills and strength. All three robots were eventually destroyed.
After the destruction of the Seed, rendering all magic gone, Andrew Wells (once a friend of Warren's) constructed a second robot duplicate of Buffy Summers and based it in San Francisco to protect the real Buffy. This replica contained Buffy's memories and did not know of its true nature until its arm broke off. It also could not mimic human functions such as digesting food, menstruating and maintaining a good balance of Ph in its blood, causing Buffy to believe she was pregnant.