Waits are represented by SQL Server wait statistics. SQL Server tracks wait information any time that a user connection or sessionid is waiting. This wait information is summarized and categorized across all connections so that a performance profile can be obtained for a given work load. You can see this data exposed in the DMV sys.dmoswaitstats.
all processes or spids go through a cycle that can be represented by the OS
Execution Model. For example, the processes waiting (in line) for the CPU to
become available are in the "runnable" queue, and the time spent here
is known as a signal wait. The spid at the head of the line gets to the CPU,
and if it has all the resources it needs to continue, it proceeds to execute
and is now "running". If however, when the spid gets to the CPU, and
the resource is not available, it get's placed on the waiter list, and is said
to be "suspended" until the resource becomes available - this
represents the wait time (or resource waits).
total time is takes for a process to complete its execution (from beginning to
end) is called the total query response time.
on above information, the total query response time can be calculated as;
Wait + Resource Wait + Cpu Time = Total Query Response Time