Pretending to work. Covertly engaging in fun activities instead of work, but still appearing as a motivated employee.
Three reasons for the origin of this word:
1) A serf was a form of slave required to work a master's land. Lower-level
employees in a modern business can also feel like slaves.
2) Surfing
the internet is a common activity undertaken instead of working
3) Surfer culture is traditionally laid back and does not value working