In reply to babanrosesalluri5:
Both Virtual sequence and Virtual sequencer are actually required to coordinate the running of sequences on different sequencers. When you have only one sequencer then virtual sequence does not provide any visible benefit,but if you have multiple agents in your environment(which is mostly the case) then you require it. Also use of Virtual sequencer is discouraged on Verification Academy because same coordination can be achieved by using virtual sequence only.
virtual sequence => you can remember it as sequence of sequencers.
also check this
http://cluelogic.com/2012/01/uvm-tutorial-for-candy-lovers-virtual-sequence/