Link Pyramid is working SEO technique in which you rank your site step wise. It works more on the mechanism of building pyramids of your link.
There are basically layers that work over the pattern of tiers. i.e. 1, 2 and 3.
The basic reason for building pyramid is to safeguard the main url from getting hit or penalized. If any Google hit comes, it will first hit the one that is near to it, it will then move to second and eventually, your site will remain peaceful and untouched.