Iframe Tag just adds another window on your Webpage and due to which whenever a browser loads a page with an iframe it loads the original Page and Iframe as a separate 2 different pages. So in some cases Iframe is not-supported and thus, displays an Error.
Sigma is a Greek letter that corresponds somewhat to our letter S and thus sigma is often used to stand for some concept that starts with S. There is an upper case (capital) sigma and a lower case (small) sigma. They are and. is most ofter used to indicate a sum.
Six Sigma is a quantitative method that focuses on improving quality in manufacturing using data collection and measurement, with the goal being to eliminate errors and variation. The result is improved product quality. Six Sigma addresses both the production and design of a product.