ERP? Well, it's not "Erp!" after too much beer, it's more like "Eeee Aahhh Pea."
For most people, ERP is a meaningless string of letters. You might (with a suspicious and nervous half-smile) ask "What are you talking about?", in which case I'd probably try to explain in as much detail as I think you could stand.
"ERP? It's software that can run everything about a business, from accounts, through purchasing, stocks, assembly, sales, deliveries, supplier and customer paperwork, customer relationships, staff ... everything, really! Some people call it business data management software, others business process management, or management information systems, and others just think it's a bit like accounting systems. They're all a part of ERP."
I could point at online resources for a definition of ERP [1 - see below], which can give the general scope of these systems.
Or I could use a related TLA [2] that everybody now seems to have heard of - CRM [3], or MRP, perhaps - and say "well, CRM is one of the most important pieces of functionality in it, especially since it's so well integrated with the accounting." (That would make us both sound rather nerd-ish and in the know, wouldn't it?)
But that, mentioned almost in passing there, is the key to ERP. It provides an integrated system, not islands of functionality, so your accounts reflect today's reality not just last month's, or last quarter's; your Sales people can see what support issues you're having with a customer minute by minute; and you can manage your whole business properly based on real information and not a guess.
When I'm asked what I do, I should first of all say "I can help you to mind your own business" and only then answer questions of how - which is by analyzing business problems and providing solutions based on Open ERP [4].
[1] ERP - Enterprise Resource Planning [Wikipedia]
[2] TLA - Three Letter Acronym [Wikipedia]
[3] CRM - Customer Relationship Management [Wikipedia]
[4] Open ERP - Open ERP Open Source Enterprise Resource Planning [website, Wikipedia]
