I was reading this page and I don't know what something means.
Fulton Armory AR Cleaning/Lubing Tips

It has the bold warning, "Do NOT put any grease on the barrel extension, chamber, bore, or the firing recessess of the bolt!"

Anyone have any idea what "the firing recessess of the bolt" means?

Bolt lug recesses would be my guess.

Yep, also the whole area where the ejector is and where the base of the cartridge sits.

Yep, the O in the site logo.

Ignore what I struck through. It is stupid.
That is one of my guesses, but the page also says to lightly grease the "bolt body including the lugs" and if you grease the lugs, some of it will xfer to the chamber extension. It would have been nice if they'd included a diagram.

I know this gets into the holy war over using grease in an AR action. In fact, the the lube guidance *is* using grease in an AR! Of course, this advocated putting down a sooper-thin layer with a small paintbrush. I can tell you from 1st-hand experience that you can put a sooper-thin layer of grease (Tetra) with a small paintbrush on the inside of the upper receiver, the insides and outsides of the BC & bolt, send 150+ rounds downrange and not have a problem.

Cleanup of the upper receiver and BCG is easy. Rubbing alcohol to wet a cotton cloth to break up the grease followed by a dry cloth to remove it seldom needs more than 2-3 repetitions before   it is all clean.

Another easy way to remove grease is to wipe it with oil. Oil will dissolve grease almost immediately and it holds the dirt as well. Oil is one of the best products to use to clean a dirty greasy surface because the oil attracts and holds the dirt. Alcohol and other solvents do not clean dirt off an object as well as oil does. As they dry, they leave the dirt on the surface metal. It is well known in building race engines that we use oil to clean every surface after machining to remove all debris; especially after honing cylinder bores. That is a separate step from lubrication for assembly.