There are three levels:
- Eager loading: you do everything when asked. Classic example is when you multiply two matrices. You do all the calculations. That’s eager loading;
- Lazy loading: you only do a calculation when required. In the previous example, you don’t do any calculations until you access an element of the result matrix; and
- Over-eager loading: this is where you try and anticipate what the user will ask for and preload it.
I hope that makes sense in the context you’re seeing it.
Let me give you a “Webby” example.
Imagine a page with rollover images like for menu items or navigation. There are three ways the image loading could work on this page:
- Load every single image required before you render the page (eager);
- Load only the displayed images on page load and load the others if/when they are required (lazy); and
- Load only the displayed images on page load. After the page has loaded preload the other images in the background in case you need them (over-eager).