Domains
A domain is a block of related information. Ideally breaking a big program up into smaller domains makes the problem more manageable.
When developing applications, consider that there may be one or more domains.
For example
Consider the n-tiered application. A UI layer, a business layer and a database layer. You could say this is 3 different domains.
Another example
Consider the employee system at SASD. Clerical editor, Employee Editor, Timesheet System, etc. Maybe you have an employee domain(s), and timekeeping domain(s), maybe position management could be broken up into domain(s)