Hp Procurves - Primary VLAN questions

Hey all

Networking noob here - but my company doesnt have a networking admin.

So, I had questions about primary vlans. I'm trying to do a VLAN cleanup (this core switch had ~18 vlans, only about 5 of which are actually in use) and I cannot delete one of them - its being cited as primary vlan.

• How does one identify what the current primary vlan is?
• What are its functions, really?
• Does there have to be a primary vlan?
• Does it matter what vlan is primary, as long as there is one?

Thanks