What is Lightbox? It is one of the best pieces of code ever written for web browsing. EVER!
But really, what is it? It's an unobtrusive Java script that overlays an image on top of a web page. It's super useful if you want to display a large image and other objects on your webpage like text and other images. You can display just a thumbnail that users can click on to display the entire image and they don't have to leave the page. You can also use it as a do display several images in a single webpage to minimize the space used and the need to scroll down. See it in action. It is also very easy to implement.
A drawback is that it takes a little more time than usual to put in images because you have to add additional parameters especially if you want to make your images SEO friendly. But thanks to my MS Excel experience, I was able to create a an Excel sheet that helps me semi-automate the process. :)