I think I now know what to call the condition of my old timber floor in Paris. It was indeed dangerous for anyone not wearing shoes or slippers with a hard sole, for you could get nasty flat splinters.

Verschiedene Rissarten und ihre Bedeutung
KERN- ODER SCHILFERRISSE, IN DER SCHWEIZ AUCH WINDRISSE GENANNT, stammen aus Überbelastungen des Stammes durch extreme Windbelastungen, Schneedruck oder auch unsachgemäßem Fällen des Baumes. Die übermäßigen Biegebeanspruchungen im Stamm sind als Ursache für derartige Risse aufzuführen. Charakteristisch für Windrisse ist ein sehr unregelmäßiger Verlauf im Holz, oft auch mit Brüchen quer zu den Fasern. Im Bereich von Windrissen stehen somit SCHIEFER- ODER FISCHKIEMENDECKELARTIGE HOLZABSPLITTERUNGEN auf, welche für die Nutzer des Bodens äußerst gefährlich sein können.
https://www.bm-online.de/wissen/bauelemente/riss-ist-nicht-g...

Langenscheidt gives Kernriss as heart shake, star shake, star check

Shakes are cracks in timber. [...] HEART SHAKE is a crack in the heartwood, near the centre of the tree. It is caused by poor seasoning, or by using trees felled past maturity.
https://en.wikipedia.org/wiki/Shakes_(timber)#Heart_shake

WIND SHAKES are fairly rare and the occur in trees that are still standing. If the tree is diseased or dead and it is losing it's natural strength then shakes occur in a horizontal direction, that is across the grain. Timber used in any structural application such as joists or rafter must not have wind shakes. Luckily they do not occur often.
http://www.builderbill-diy-help.com/timber-defects.html

Shakes are natural occurring defects in standing trees caused by a lengthwise separation of latewood fibers. Shakes were once thought to be caused by external stress factors such as wind and temperature extremes (often CALLED WIND SHAKES); however, research has found that a bacterium is the true cause of shake. The bacteria that causes shake enter the trees through the roots and not through the stem. The bacterium belongs to the clostridium genus and is often accompanied by an unpleasant odor.
https://blog.spib.org/shakes-checks-and-splits-in-dimension-...

" For new floors, we spot fill staple holes, nail holes, chip outs, and any gapping between floorboards. Any wind-shake or blisters are fixed using epoxy."

"SLIVERS AND/OR SPLINTERS ARE PROTRUDING FROM THE SURFACE OF THE FLOOR, especially at the edges of the boards. CAUSE: • Unevenness caused by expansion, cupping, subfloor irregularities, edge crushing from expansion or grain raise from moisture. • Damage during installation associated with nailing. • WIND SHAKE (associated with annual rings/springwood fractures). • May tend to occur more frequently in beveled prefinished products and wirebrushed products. • Improper grading [ ... ] FOR WIND SHAKE, it may be possible to repair the boards using LOW VISCOSITY, CA (CYANOACRYLATE) ADHESIVE (such as Super Glue). Apply the adhesive under the seam of the shake. The adhesive will wick down and hold the shake. Because it is clear and nonambering, it can even be used between coats of finish. Or, the boards can be removed and replaced"