How would you explain EDA to your grandma?

Grandma, until EDA, most computer systems exchanged data in "batches" - all the events from the last day.
With EDA, the data is forwarded as it comes in. So they can tell the difference between something that sold out 3 hours after the truck delivered to the store, and something else that sold out just before the next truck arrived. Please! Order more of the first one!
Also, there is finer levels of control. You can send the data about Nikelette Socks to Nikelette, as it happens. Maybe you want to filter out from their stream all the messages about transactions that they were in that were started and then cancelled because the customer's credit card didn't work.
You definitely want them to know about returns, though! So you can have policies about, for instance, what message types go to suppliers.
You want to have message types that support the filtering you need.
This type of system sounds complex, and it is. You need to plan it. You need to have input from different parts of your company and from people who deal with suppliers, customers, government rules, etc.
It is a major project for a company to switch to this type of system, but it is totally worth it for large companies, and even many medium sized companies.