What is the difference between an insert window and a standard, full frame window?

Q. What is the difference between an insert window and a standard, full frame window?

Q. Can I get Bilt-Best replacement insert window sashes?

A. An insert window is installed into the existing window frame - saving you a bundle of money in time and construction costs. Insert replacements for old Biltbest units are available in casement, awning and double hung styles.

For Casements: http://www.biltbestwindowparts.com/content/biltbest-replacement-casement...