Hello Manish
A DHCP renewal occurs when a DHCP lease expires. The DHCP host will contact the original leasing DHCP server and request a new lease. A renewal simply renews the lease time. The actual IP address and the MAC address in the server entry, and any DHCP options used all remain the same.
A rebinding is when a host will remove all network information it may have previously obtained from a DHCP server and will begin from scratch. This is essentially the same process as a host would use when it initially powers up. It sends out a broadcast asking for a DHCP server to respond and binds to the server that responds successfully. In this process, it relearns IP address, subnet mask gateway, DNS server, and any options that may be made available.
When a host attempts to perform a DHCP renew and it fails for some reason, it will then attempt a rebind.
I hope this has been helpful!
Laz