system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is “Sigma” such a pervasive word in business? Six Sigma, Two Sigma, lean sigma...
gpt
Let's use a manufacturing business as an example...

Everything you make has a target specification range. This could be width, weight, etc.  For example the product should be between 2mm and 4mm thick.  

In a perfect process, your mean would be exactly in the middle and never shift.  That never happens though. Variation is inevitable. More variation means more products you have to scrap.

How much variation you have can be measured and plotted on a curve. We can then see how many standard deviations exist between our mean and our spec limits.

Sigma is the mathematical notation for standard deviation. Six sigma is having 6 std deviations between the mean and spec limits. 

If we can achieve 6 sigma, then we'll only have 3.4 defects per million opportunities.