Soap is just low quality hashish made with any shit they feel like using , it usualy comes wrapped in celophane and is distinctive in it's hard texture and tendency to ball into hard lumps , as opposed to good quality hash which is softer and crumbles smoothly.
Soap can be spotted in a couple of ways , when heated it gives off a distinct smell not unlike burning rubber and it is darker than most hash ( some exceptions such as good quality squidgy are also dark) .