What is OWA means?
OWA "front End" " DMZ Area"?
OWA "Back End" " DMZ Area"?

OWA has always meant Outlook Web Access to me. That's the Exchange service that allows users to use the internet to access their corporate mail outside of the corporate network.

Need is absolutely correct. OWA is Outlook Web Access.

DMZ is a Demilitarized Zone, separate area between the internet and the internal network.

Front end and Back end are probably refferring to outlook servers, front end deals with user requests and the back end typically holds mailboxes and public folder stores.

DMZ usually stands for DeMilitarized Zone. In network terms it refers to a PC on a network that is left outside the firewall.
I also agree with NK on OWA. Why are you asking?

Thanks (Need, StuMegu and Scott ) I Think It helps and now I anderstand.
Some one gave me more clear picture the mean of OWA ? Which means
A Web based version of the normal Outlock.

Thanks

Here's a screenshot of OWA (http://www.iitk.ac.in/cc/windows/outlook2003/owa-screenshot.jpg).

Actually Front-End and Back-End refer to the networks that are considered either inside or outside your organization. It makes more sense when you have two Network Interface Cards (NICs) on the OWA server where you designate one NIC as Front-End (i.e. facing the Internet) and the other NIC as Back-End (i.e. facing your internal network). So this server would be dual-homed and would have a Front-End and a Back-End connection.

Some installations only use one NIC and designate (via IP addresses) what is considered Front-End and Back-End.

EDIT: Or you can put both NICs on the same DMZ segment with different IP's which is not recommended.

Thanks Cajalat, your explanation make more clear to me.