Pocket Edition servers are Minecraft servers that are available for the Minecraft pocket edition. These run Minecraft on a phone, kindle, or other handheld device instead of your standard Minecraft pc version. Pocket Minecraft uses pretty much the same code as Minecraft pc edition so a lot of mods that work on the pc version will work on pocket Minecraft but not all of them.
Pocket Minecraft servers are also available in creative mode where there are no monsters and the whole world is made out of blocks which provide infinite resources, in survival mode, this would just be boring because there are no monsters killing you and Minecraft would just become a mine building game.