Thanks David. 
I am new to Wireless. My CCNA expired a long time ago. Now I am preparing for CCNP ENCOR.
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Hello Gowtham
Mobility Groups and RF Groups are entities that you must create whenever configuring WLCs. They are especially useful when you have topologies with multiple WLCs that you want to work together.
A mobility group for WLCs is used to enable seamless roaming of wireless clients. When the same mobility group is assigned to multiple WLCs, it allows wireless clients to roam between APs that are registered to different WLCs. When WLCs are configured in the same Mobility Group, they establish a trust relationship. They share critical information about connected clients, including MAC Address, IP Address, VLAN, security session keys and context (e.g., 802.1X/EAP authentication state), and QoS Policies. When the user roams from AP-1 to AP-2, the client’s session information is passed from WLC-1 to WLC-2 over a secure Mobility Tunnel. WLC-2 now has the client’s full context and can immediately bring them onto the network without requiring re-authentication. The client’s IP address is maintained, and the Wi-Fi session continues without interruption, i.e. seamless roaming.
The RF group is another entity to which multiple WLCs can belong. An RF Group allows a group of WLCs and their associated APs to operate as a single, coordinated system for managing the radio frequency spectrum. This is a dynamic and automated process. This allows the group of WLCs to optimize the physical radio layer for performance and stability automatically. As long as the RF group name is the same, the WLCs will handle the rest.
In the lesson, the RF Group and the Mobility Group seem to be a single configuration parameter. In newer WLC versions (9800 series) these are separated into two entities, and you can configure them separately, allowing a WLC to join a mobility group with certain WLCs and an RF group with other WLCs, giving more flexibility.
I hope this has been helpful!
Laz
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