Hi Sumita,
An inproc is one, which runs in the same process area as that of the client giving the advantage of speed but the disadvantage of stability because if it crashes it takes the client application also with it. Outproc is one, which works outside the client's memory thus giving stability to the client, but we have to compromise a bit on speed.
Please refer the below links
http://www.codeproject.com/KB/session/ASPNETSession.aspx
http://www.codeproject.com/KB/web-cache/cacheinwebfarmandwebgarde.aspx
Thanks