6-Axis robots are robot arms with 6 points of free movement. There are also robot arms with fewer axis configurations but these are not as common, a 6-Axis robot offers more flexibility. The 6 points of the axis typically start at the base of the arm to what is essentially the wrist of the robot.
How are they different to Cobots?
6-Axis robots are industrial size, working with weights over 15kg and far beyond this, whereas a cobot is picking up weights under 15kg. A cobot can work alongside a person, unlike the 6-Axis robot which is independent and is usually operating behind a cage/guarding.
Speed is another factor why you might use a 6-Axis robot as they can operate at much higher speeds.