Though we don't recommend using iFrames, there are two possible answers to this question.
Can I embed a dashboard into my website?
Yes, it's possible to use an iFrame to embed a Geckoboard dashboard into a website (i.e. having different pages with different dashboards) using a Sharing link. The code should look similar to this (although you will probably want to add height and width parameters):
Can I use an iFrame to embed content into my dashboard?
No, you cannot embed online content into your Geckoboard dashboard via an iFrame. Here you'll find the different methods to get data that we support on to Geckoboard. You might find particularly useful the Image widget, if you want to embed an image and the Text Custom widget if you want to embed messages and/or other HTML content.