Timeout is important session state setting in the web.config file. It specifies the number of minutes that ASP.NET will wait, without receiving a request, before it abandons the session. 
<?xml version=”1.0” encoding=”utf-8” ?> <configuration>      <system.web>      <!— other settings are omitted. —>      <sessionState         cookieless=”AutoDetect” cookieName=”ASP.NET_SessionID”         regenerateExpiredSessionID=”false”         timeout=”20”         mode=”InProc”         stateConnectionString=”tcpip=”         stateNetworkTimeout=”10”         sqlConnectionString=”data source=;Integrated Security=SSPI”         sqlCommandTimeout=”30” allowCustomSqlDatabase=”false”         customProvider=””      />      </system.web> </configuration>
 This parameter is one of the most important, because a difference of minutes can have an impressive effect on the load of the web server and performance of the web application. Ideally, software developer should choose a timeframe that is short enough to allow the server to recover valuable memory after a client stops using the application but long enough to allow a client to pause and continue session without losing it.Software developer can also programmatically change the session timeout in code:Session.Timeout  = 15;