System integration
System integration connects the programs a company already runs so that data moves between them without being re-keyed. It sets the direction of each flow, the data format, and which system is the source of truth for a customer, an item code and a price.
A typical set-up in a company of 20 to 500 people is an ERP (Comarch, enova365, Subiekt, Streamsoft, SAP Business One), a shop or sales platform, sometimes a WMS or a carrier system, plus a handful of spreadsheets that exist because something was missing from the systems. Integration removes none of them. It organises the traffic between them and takes the re-keying away from people.
Most of the effort goes into mapping the data, not into the connection itself. The same customer is "P.H.U. Kowalski" in one system and "PHU KOWALSKI SP. Z O.O." in another, item codes use different symbols, units and VAT rates are recorded differently. Those decisions belong to the company rather than to the software vendor, and the schedule should leave room for them.
When the system on the other side has no API, the integration works with what exists: a scheduled file export, a database read, an import in the vendor's own document format. It works, but it is more fragile under any change, so it needs a retry queue, a separate error queue for manual decisions, and an alert when the file did not arrive at the agreed time.
The signal that this is your problem: two systems show different stock, customer service checks an order status in three places, and onboarding a new employee is mostly teaching them what to copy from where to where.