A database is a program to store “structured” data.
Just to compare, non-structured data:
A directory with tables, images, texts.
Structured data, <Name, Age>:
Structured data may be extracted with higher data extraction speed. Imagine a directory containing a million of files with ages. To find Mike’s age you have to sort out all these files. It will take a lot of time.
A database extracts the data almost instantly.
Most Internet texts are stored in databases. Bank transactions are stored in DB as well.
The first blockchain implementation, Bitcoin, was a special database. This database had some unique properties.
Decentralized applications are installed on many computers and there is no “central computer”.
The centralized apps are an alternative.
Any bank has central computers.
Applications on desktops of bank officers or mobile apps of the clients intercommunicate with the central computers and each computer has its unique role and rights in the system.
In contrast to this, any torrent system has no center.
Blockchain is an example of a decentralized system.
Blockchain software is installed on “blockchain nodes” and all nodes are equal, and the system contains no central node.