A parent iframe is an internal frame in a web page that holds a secondary web page or script. They are often called iframes, since the "parent" part of the name is from the viewpoint of its content. Anything in an iframe is considered its child, while it is considered the parent of its content. These frames can be placed anywhere on a page and can be any size.
If a static web page is displayed, most web designers put some type of border around the parent iframe to distinguish it from the outer page. The URL of a static web page inside the frame may be any valid Internet address. Essentially, iframes allow two web pages to be shown at once. Displaying multiple web pages in coordinated iframes is a relatively common method of web organization.
The most common use of a parent iframe is to run a script that adds dynamic content to a web page. Iframes can run PHP, Perl, or JavaScript scripts equally well. With the internal frame's ability to embed scripts, web developers can process data, flip through images, show videos, embed media, and perform a variety of other functions that static web pages don't allow on their own. While there are other ways to embed scripts and dynamic content into web pages, a parent iframe often minimizes the amount of extra markup needed for those pages.
Working with a parent iframe sometimes raises compatibility issues with client browsers. Most modern web browsers support iframes but not all older browsers do, so web developers must often take this into consideration. Workarounds are possible, but these workarounds are rarely able to replace iframe functionality. Depending on the desired iframe functionality, the workaround may be as simple as showing an error message or as complex as a completely new script call.
A parent iframe can run either server-side scripts, which depend on the computer hosting the web page, or client-side scripts, which depend on software installed on the user's computer. Server-side scripts can always rely on the proper software being present, so an iframe will almost always be filled properly regardless of the state of the user's computer. Client-side scripts may not work at all if the user doesn't have the proper software, which might result in an empty or error-filled iframe.
In general, parent iframes are robust and useful additions to most web pages. Issues with server- or client-side scripts can be handled with appropriate preparation, making significant errors in the frames unlikely. An ongoing debate exists over whether or not iframes should be considered good web programming practice, but their use is almost always a matter of personal preference on the part of the page designer.