Can you help explain what this means?

Above the fold content?  Is that like a fold in a sheet of paper?

Yes, it comes from the advertising/marketing industry.  It's like what you would find on a sheet of paper for example, folded to fit in an envelope for mailing.

 Above the fold just means what you see in your browser when you first load the page before having to scroll down.

"Above the fold" content on a website is regarded as being the most prime real estate on your site as it is what everyone sees first when they visit your page. You want it to be content that grabs visitors' interest to entice them to scroll down and go further into your site. You'll also want your most important message here in case they don't.

In the comparison to the sheet of paper example; if you get a letter in the mail, take it out of the envelope and read the part above the fold and determine that it is junk mail with an offer that doesn't interest you, you'll probably throw it out before ever unfolding it to read the rest. Also, like a newspaper folded on the store shelf. If the headline appearing above the fold catches your eye, you're more likely to buy it.

Thanks for that that is helpful but what about the rest...