There is no generally-agreed definition, but I would use the word "robot" only for machines that have manipulators (i.e. some equivalent of arms with hands; something similar to octopus tentacles or elephant trunks also qualifies as a manipulator).

Originally "robot" was used only for humanoids, but the only essential capability that distinguishes robots from earlier machines are the manipulators, so in all other respects they may not resemble humans or animals nowadays.

Maybe “an automated thing that moves to do stuff”. Generally there are manipulators and mobile robots like vacuums. An interesting edge case would be a CNC machine which has degrees of freedom similar to a pick and place robot but is seen as a whole static thing with moving parts. Also if the mobile platform transports people it’s usually not called robot.