Best practices - when can you say a practice is a best practice?

Whenever you search on database performance tuning, the frequently uttered word is to follow best practices. What is this best practice? When can you say a practice is a best practice? Those were 2 questions putup for me when I referred the BP in recent usergroup meetings, all the blog posts here are inline with my experience and sharing knowledge that focuses on the best practices which I apply (and encourage our technical clients to employ) when developing, designing &amp; fine tuning any data...(<a href="http://sqlserver-qa.net/blogs/el/archive/2010/09/15/9554.aspx">read more</a>)<img src="http://sqlserver-qa.net/aggbug.aspx?PostID=9554" width="1" height="1">