It is a common question asked by many users that what exactly we mean by SharePoint Farm? The answer is
A SharePoint Farm is a collection of all those SharePoint servers that share the same SharePoint configuration database.
By Default, configuration database name is SharePoint_Config. As per Microsoft TechNet article here, configuration database is the fundamental SharePoint database and used for following:
- Contains data about all SharePoint databases,
- all Internet Information Services (IIS) Web sites or Web applications,
- Trusted solutions,
- Web Part Packages,
- Site templates,
- Web application and farm settings specific to SharePoint 2013, such as default quota and blocked file types.
- Must be co-located with Central Administration Content database
- Only one Configuration database is supported per farm.
- Scale up only, significant growth is unlikely.