A database is searchable collection of information. When you are working on an assignment or paper, you will be searching library databases. Library databases are searchable collections that may contain articles, newspapers, books, and other materials that you may not be able to find on the open web. The library pays for access to these databases.
Omni is a great database for getting started, especially for multi-disciplinary topics. If you want to get more focused results, try thesubject-specific databases. Check out your program's Research Guide for more database recommendations.