Link exchange is one of the earliest and most popular SEO technique among smaller websites to get inbound links (urls pointing to your website). Basically, what a web master does is to exchange urls of his website with another website. There are a few variations to link exchange, ie it could be 2-way, 3-way, 4-way...etc. 2-way link exchange means site A exchange links with site B (This is the most common definition of link exchange). 3-way means A link to B, B link to C, and C link to A. You could figure out the rest of the variations easily...