Cold Solder Joint
Cold solder means the solder is more or less in the right place, but isn't actually bonded to one or more of the metal surfaces in the joint, so the solder bond will be poor and the cracks may develop in the joint over time. A cold joint is one where the solder did not melt completely. Thus, it is unreliable and often characterized by a rough or lumpy surface. It can also happen when you're soldering materials that haven't been prepared for soldering. For example, bare aluminum is a real pain to solder.
To prevent cold joints, make sure every surface you want to solder is actually being heated to the melting point of the solder. If you're using a soldering iron, it should touch every metal surface in the joint. Don't use the iron to melt the solder. Wait for the heated surfaces to melt it.
If you still find cold solder joints on you circuit board, don’t worry. They can usually be repaired by simply re-heating the joint with a hot iron until the solder flows. Many cold joints also suffer from too much solder. The excess solder can usually be drawn-off with the tip of the iron.