Spawn Camping is an act of attending a respawning player and overwhelming him, while having low interest in caping the flag. This behaviour is frowned upon by most players and often results in bad chat language and being hunted by the affected heroes.
The difference to Base Camping is that it is has not neccessarily the backbase location and be executed by multiple players.
Most common way is to move undiscovered behind the enemy lines and camp for respawning players. If one appears he's intantly attacked and having a low chance to escape due the surprise moment.
Spawn camping is usually common for both teams in Seaside Skirmish throguh the use of tanks. Bucaneer Bay favours spawn-camping with tanks, particularly in favour of the Nationals.
Server Admins can include prohibits in their serfer rules and kick for that reason. The best way to help yourself is not to trust on being safe after a respawn.