View the link for information on knowledge base. And I hope you know what is a database.
Anyway here I am writing a small description on database.
A database is an organized collection of data. Here organized means, the data is formatted and stored in a certain manner and each data entity in the database is meaningful in a certain way. For more information check the link.
A database is an information store which holds information. A knowledge base is an application which displays information is a useful way which can be used by people to do something (usually fix problems). A knowledge base will use a database as a backend to store the information within it.