In an English climbing guidebook about a French region, I read the term spit anchor in the general description of the equipment of the (multi-pitch) routes of some crags. I never heard that term before; what is a spit anchor?
Searching the climbing dictionary for "spit" shows that this is the french term for a "bolt".
So the answer is simple: The translation of the guidebook isn't perfect. "Spit anchors" are bolted anchors (or rappels) on these routes. (Which actually matches my observation there.)
A spit is not just any bolt. Spit means almost exclusively (especially among cavers, who care more about the what they are clipping into) the hand-drilled bolts now sold as Cheville autoforeuse by Petzl. They used to be sold by the Spit company and AFAIK they are still made by them but are sold by Petzl. The Spit company still sells a lot of industrial bolts, but no climbing certified bolts.
Nowadays Petzl sells spits for caving single rope technique use, not for climbing and mountaineering.
They usually use the thin M8 thread, although wider designs existed. They may require bringing your own hangers (8 mm, sold by Petzl as Vrillee, Coudee and Clown). If the hangers are in place they should be tightened by an M13 wrench before use.
The spits are prone to rust and on old routes they cannot be trusted 100 %. They are very short, because they are drilled by hand and are sensitive to the exact depth of the hole. If the hole is too deeep, the hanger will be pushing the bolt out of the rock.
Cavers never use spits (even new ones) as a single point anchors. On top of a pitch they should always be doubled.
To add a little to Vladimir F's good explanation of Spits......In climbing and mountaineering, in Spain/ France at least, Spits refers to the old type of bolt that was often drilled to a very shallow depth. Because of their age and shallow depth any climber these days (post 2000) should really try his or her hardest NEVER to take a fall on one of these..... If you hear/read that a route is "protected" with spits.... you should interpret this to mean: "bring your own trad protection, or be prepared for some very scary pitches that you can not risk a fall on"