Define the term Sigma in Six Sigma

Naveen…I had a so called smart butt black belt once ask me to define Sigma…and i asked which one?Normally Sigma in statistics is the Standard Deviation of the Population or basically the spread of the values about an average or middle value (mean, mode, medium or geometric). Therefore you tend to have a + and a – value. e.g. +/- 3 Sigma (but you may have +4 and -2 for skewed distributions)…which is 6 in total and where Six Sigma(TM) comes from.In Six Sigma(TM) talk, it is a similar thing, but you start at 0 and everything is plus (+). Like the cumulative of the values so you remove the negative s and a comparison between Sigma’s can be made (In theory)That said i have work at some so called leading companies where BB’s and MBB’s get negative Six Sigma(TM) Sigma values, which is impossible. The reason…because they use an Excel equation called INVNORMDIST! Which is wrong.Boring stuff, but if you’re feeling suicidal one day and need a distraction, you can plot this Excel equation and compare it to the Yield values that Six Sigma(TM) uses. You will see that they do not correlate at all, except at 50% defect rate.That said, today the sun is shining bright and i would not waste your time. Enjoy the day. Life’s too short.

Really.
That is as bad an answer as I have ever seen on here.
Naveen – read the new to Six Sigma? in the blue bar to the left.

That is just as bad a reply as that previous idiot.
There is only one meaning of sigma … the one used for control limits. 

I suppose what I should have said explicitly was that his assertion that the “6” in 6 Sigma came from the +/- 3 sigma control limits he described below was wrong.  6 refers to a measure called sigma level which refers to the Z-table.  This is a count of the number of standard deviations that can fit between a mean and a target value.  +/- 3 Control limits refer to the Shewart Control Chart limits placing a UCL and LCL at 3 standard deviations from the mean.  Sigma Level and Sigma are not the same thing.
Normally Sigma in statistics is the Standard Deviation of the Population or basically the spread of the values about an average or middle value (mean, mode, medium or geometric). Therefore you tend to have a + and a – value. e.g. +/- 3 Sigma (but you may have +4 and -2 for skewed distributions)…which is 6 in total and where Six Sigma(TM) comes from.
Please excuse my poorly worded response from the last post.

Hal – I know you know the difference between sigma level (from the standard Z tables) and standard deviation (sigma).
Not trying to pick are you?

Thanks Phil.  I certainly wasn’t trying to get into that argument.  Just wanted the previous poster to know that there was a difference.