Many websites depend on advertising for revenue. Google does know this, even offering its advertisement placement service, AdWords. However, not absolutely all types of ad placements are regarded equally.
Google considers some advertising tactics disreputable or spammy and can penalize sites that utilize them. It is critical to know which types of advertising are acceptable, and those have the potential to truly get you in big trouble.
"Above the fold" identifies what a viewer can easily see whenever a page is first loaded. A viewer typically visits a webpage for this content, plus they expect content to be first thing they see. When there is only advertisements above the fold, with the actual content buried somewhere below it, then your page is not smartly designed.