Can any one let me know what is the difference b/w customer interface and user interface??one of our client has raised this question ,whether we can create a customer interface and application in salesforce.
I would guess that your client is talking either about communities or Sites, both can be used to be Customer facing.
As a pictured sample the ATM is the customer interface of a bank society so you as the customer can interfacing with their service to manage your account.
The ATM itself has a user interface to enable the user ( you) as a human to communicate with the system (Computer)
In Salesforce terms I would say the user interface you mentioned is the one who logs into Salesforce in the office to work with (standard page layout, licensed User), while the customer is the client of that company where you just logged into (not licensed) accessing your objects ( cases) through a public website, where you define what the customer can see
hope that helps