A database is a structured collection of data. The structure of a database can take many forms, including relational databases, NoSQL databases, and search indexes. Data stored in a database can be either static or dynamic. Static data does not change over time -- think of the contact information you have on file at your ISP or credit card company. Dynamic data changes frequently, such as the current balance of an investment account or the number of likes that a social media post has received since being published.
Database administration is a massive topic that can be subdivided into sub-categories of database techniques including security, performance tuning, data modeling, schema design, and backup. Database development is also an important subset of database topics related to the creation of data models for new apps. These articles are often written by database administrators or software engineers who specialize in database development.