What is OLP NL in server licenses?

OLP = Open License Program
Microsoft Open License is a Volume Licensing program for small to midsize organizations that have fewer than 250 desktop PCs. The program provides a simple, flexible, and cost-effective way to buy the latest Microsoft technology to meet your organization's needs and procurement procedures.
http://www.microsoft.com/licensing/programs/open/default.mspx
NL = No Level

Some Microsoft Volume License programs have "Levels", which are basically bulk discounts. Some other companies call these "price bands". Depending on the number of licenses purchased at once, discounts get applied. If you don't purchase enough for a discount, this is called No Level or NL.

For example:

Microsoft Exchange Server 2007 Standard CAL has two discount Levels:
No Level - for 1 to 49 users
Level C - for 50+ users