From Second Life Wiki
How To Camp / What Is Camping?
Camping is when somebody pays you to sit (or dance, or sweep the street, or wash the windows ...) at their land; the longer you stay the more you earn. Typical rates are L$1 per five to twelve minutes. At today's exchange rate, you would need to camp for at least 23 hours to earn one U.S. dollar.
Camping typically happens in shops, malls and clubs, and the reason it occurs is that the owners want to make their place seem more popular than it really is. Statistics on sites' traffic are published regularly, e.g. on the "popular places" tab of the Search window, and the owners are paying you (the camper) to help them cheat the system. Don't feel too bad about camping, though: everyone has done it for some amount of time, at least when they were newbies.