What an ERP system actually is.
ERP is not a list of modules. It is one shared way to run finance, sales, inventory and operations on the same facts.
Most explanations of ERP start with a menu of modules: finance, sales, purchasing, inventory, manufacturing. That list is useful, and it is also how companies buy the wrong system. An ERP system is the place where the company agrees on one version of what happened.
One set of facts
When sales closes an order, finance should not retype it. When the warehouse ships, inventory and the customer invoice should move together. ERP exists to stop the same fact living in five spreadsheets with five different numbers.
If your teams still export to Excel to answer "what did we sell last month?", you do not have a system of record yet. You have a filing cabinet with a login screen.
What ERP is not
It is not a report. Reports are a result of clean transactions. It is not a project plan, and it is not a substitute for a process owner. Software will not decide who is allowed to change a price, who approves a purchase, or what "available to promise" means in your business. Those are management decisions. The system only makes them stick.
It is also not automatically "digital transformation". Installing ERP without changing how work is handed over is an expensive way to keep the old company.
When a company actually needs one
You feel the need when growth creates contradictions: the warehouse says the item is there, finance says the margin is different, and the customer has already been promised a date. That pain shows up earlier in product businesses and later in pure services, but the test is the same. Can two managers look at one number and trust it?
Start there. Name the decisions that are currently made from conflicting data. Those decisions, not the vendor's module list, are the scope of your ERP.