A terminal-file in Forms is like a key-configuration-file in other applications. In Client-Server Mode it was set by environment or registry-variables. In Webforms you have the possibility to add it to your servlet-parameters (edit some files...) or you can put it in the formsweb.cfg the easier way.
Here a example:
[sepwin]
separateFrame=True
lookandfeel=Generic
otherparams=term=C:\oracle\FRHome_1\forms\fmrpcweb.res