Base Camping or Base Rape, less known as Uncap Killing (from attacking the uncapable backbase flag), is an alledged tactic seen ever since Battlefield 1942, possibly further back to games such as the original Team Fortress mod for Quake, when the first winning side decided to keep the losing side locked in their base.
It's often confused with Spawn Camping that describes the pure action to attend a respawning player and overhelm him.
The method for Base Camping is simple: When one team has been reduced to their permanant spawn on a map such as Victory Village or Seaside Skirmish, the opposing team often rushes the permaspawn as players respawn from their prior deaths. Battlefield Heroes somewhat averts this, in that players on the 'camped' team are sometimes dropped behind enemy lines, though the varied nature of the airdrop points often cause one or two troops to appear behind the "thin red line", so to speak. Since they often are secluded from the rest of the team, a single Tank, sometimes with a Gunner on support, can often finish off the airborne force before they can take an alternate spawn, sending them back to the permanent spawn, where the rest of the enemy team is waiting for them.
Base camping is usually an indicator of the impending victory of the campers over the team as in order for camping to be at a player's initial spawn point, the enemy needs to have captured all the control points. In addition, the troop reserve count drop dramaticaly at this time and the kill rate generally means a game will finish very quickly.
Most all maps beside Perilous Port Winter have measures in place to prevent one team from spawn camping the other. Their spawn areas are covered in Dead Space. If a National tries to enter a Royal spawn base then he will be killed after a period of time (10 in Midnight, 10-15 in Alpine)
For the other maps, this is best countered by just leaving the server, hoping to find a more friendly server. If only one or no hero remains in the team, the round ends and Pregame is launched, so the camping team has to wait for new player or change the server as well. Wether leaving the server during base camping is considered Rage Quit or rational procedure, highly depends on the definition and cirumstances.
Further possibilities are to join again with a higher leveled Hero, request enforcement by a strong friend, ask the admin for balance or simply get your own server.