An ERP (Enterprise Resource Planning) is software that brings together, in a single database, all of a company's management functions: customer relationship management, quotes and invoicing, inventory, purchasing, accounting, human resources, projects, maintenance, and more.
The main benefit of an ERP is integration: a piece of information entered once (a sale, for example) automatically flows through to the other modules (stock withdrawal, accounting entry, statistics). This avoids re-keying, parallel Excel files and discrepancies between departments.
A modular ERP lets you turn on only the functions your business needs, then add more as you grow. This is eyeot's approach: a common core (CRM, inventory, invoicing, finance) plus business modules that each organisation can activate.
For a small or mid-sized business, choosing an ERP comes down mainly to functional coverage, regulatory compliance (electronic invoicing, the GDPR, data hosting) and ease of use.