I understand that time slices are time slots given to processes (or threads) to execute. After the completion of the time slot of one process, its put to the end of the queue, and the next process in the queue gets to execute. But in this site : Linux Process Scheduling Modification, they are differentiating between time slice and quantum. Quantum they are saying is something inside a time slice (each process has a share in the time slice of every process). This is the quote :

every process has a specified time quantum whose duration is computed when the time slice begins. In general, different processes have different time quantum durations. The time quantum value is the maximum CPU time portion assigned to the process in that time slice. When a process has exhausted its time quantum, it is preempted and replaced by another runnable process. Of course, a process can be selected several times from the scheduler in the same time slice, as long as its quantum has not been exhausted

Its also given here

I can't understand the difference between time slice and quantum here.