(noun) the current known, accepted and generally practiced (as in "done") way of doing something in an industry or craft.

Examples:

• A "best practice" of accounting might be the double ledger system.
• In high jumping, the best practice is called the "Fosbury Flop".
• In combatting AIDS, I think it's called "combination therapy".
• Last I heard, in building CMOS chips, it was "Silicon On Sapphire", aka "SOS". But this changes daily or so.
• For measuring distance very accurately, I think it's laser interferometry.
• For sorting arrays in a program, it's (usually) an algorithm called Quicksort.
• In the Linux world, best practices are often captured in HOWTOs.
• If you're building an empire, it might be Divide and Conquer
  (which happens to be the basis for QuickSort as well).
• In guerrilla warfare, it might be hit and run.
• For spanking, it's called OTK.

I'm not an expert on any of these things, so if I'm way out of date or way wrong, please don't jump on me. I just wanted to give you an idea.