A hive is where an alliance gathers their colonies together to protect each other. They will all relocate into a tight cluster directly next to one another because it allows them to have a FOB (Forward Operating Base) if you will.
A camp wall is when an alliance has already formed their hive, then they make camps to block out anyone else from making OPs near their hive. Here is a picture to show both. You do not need a camp wall for it to b a hive, thats just a strategy some players use for added protection, at a high resource cost.
All the players inside the hive and camp wall are friendly. All other players are conquered and force relocated out so there is no chance of being attacked within the wall.