Yavapai College Library
A database is essentially a collection of information. Many library databases are simply collections of journals and other scholarly materials. So, when we talk about databases, we're talking about places you can go to search for academic articles!
Databases can be subject-specific. This means the material found in the database is geared toward a limited range of disciplines. Social Services Abstracts is a database that indexes primarily journals from the field of Social Work. You wouldn't bother checking that database if you were doing a project on sea turtles.
Databases can also be multidisciplinary. This means that the material found in the database is wide-ranging, and may cover an extremely broad range of topics. Web of Science is one example, but there are others. You could certainly find information on sea turtles in Web of Science, but you could also find information on cartooning, for example (or Social Work!).
These databases can be used to search for information on a wide variety of topics. They are great starting points for research, especially if your topic crosses into different disciplines and is a little hard to pin down.