In simple terms, a window frame is a structure that supports the glass panes in a window. It is made up of various studs with different functions. This provides strength to a window, allows it to fit in a wall easily, and helps give whatever shape or design is required to the window.
Support studs and those in window sills provide support to the window from the bottom. King studs, also known as jack or trimmer studs, offer the same support from the sides, and header studs, along with other vertical supports, work as supports for the window's top side.
It is essential to ensure the frame is not too loose or too tight. A loose window frame will allow moisture to enter the wall, whereas a tight frame can contract with the passage of time and break the glass.