IFrame's are embedded inside another page on a website. The IFrame is often used to insert content from another source, such as an advertisement, into a Web page. 

An advantage of using IFrame's would be there ability to change one part of the page while keeping another part of it static, another advantage is that they tend to reduce bandwidth as the same content does not need to be loaded every time a new page is visited.

Although IFrame's can be used to your advantages, there are some disadvantages. One of these may be that the user can only use one URL per IFrame, for example if the user booked a room at a hostel they could then go ahead and book another product with in the current IFrame. Another disadvantage is that they haven been know to be less responsive and more vulnerabilities to attacks. Also 

In this example of how we use IFrames, the client needed to have their current booking process placed in a IFrame but the rest of the website to be created through MySites. This enabled the client to keep there secure, reliable booking process but also allowed them to have the rest of their site on MySites.

The first image below is taken from the website 

This second image is the IFrame that was created to fit in with the rest of the website

 As You can see from the example above, both pages look very similar and the IFrame fits in well with the rest of the website.