Grid computing has to do with storing plenty of amounts of data through the virtualization of computer resources, while cloud computing has to do with an application accessing resources indirectly through services over the internet. When talking about grid computing, resources are known to be distributed over grids, while resources are known to be centrally managed in cloud computing.
Grid computing is usually implemented in application-oriented resources, while cloud computing is generally oriented in service-oriented resources. The resources in grid computing are distributed among several computing units to process a single task. The computing resources in cloud computing are centrally managed and put over several servers in clusters.
Grids are usually owned and managed by a single organization within its premises, while cloud servers are generally owned by infrastructure manufacturers and are placed in locations that are physically disparate. The former operates majorly within a corporate internet, while the latter can be accessed as well through the internet.