Glossary
Database
The single place where your structured information lives: contacts, files, invoices. Every piece of data has one place, and only one.
A database organises information into connected tables: contacts, their files, those files' invoices. Every piece of data exists once, in a known place: the opposite of twenty spreadsheets contradicting each other.
You already use some: every tool has its own. An SME's problem is never having databases, it is that they ignore each other. When we build a system, its backbone is a database of yours, in your name: the one that gathers what your tools know, and where your numbers come from.