From the MS Website:

Status Meaning

Background: SPID is performing a background task.

Sleeping: SPID is not currently executing. This usually indicates that the SPID is awaiting a command from the application.

Runnable: SPID is currently executing.

Dormant: Same as Sleeping, except Dormant also indicates that the SPID has been reset after completing an RPC event. The reset cleans up resources used during the RPC event. This is a normal state and the SPID is available and waiting to execute further commands.

Rollback: The SPID is in rollback of a transaction.

Defwakeup: Indicates that a SPID is waiting on a resource that is in the process of being freed. The waitresource field should indicate the resource in question.

Spinloop: Process is waiting while attempting to acquire a spinlock used for concurrency control on SMP systems.

-Dan