Modern writers frequently refer to this sort of shield as an écranché shield.
However, I've yet to see a pre-1600 source that used the term to describe a shield. This sort of shield was however, not infrequently called a targe or some variation of the term, as opposed to shield or escu. In Froissart's account of the announcement of the jousts at St. Inglevert, the defenders state that "outside of our tents will be hung our shields, blazoned with our arms; that is to say, with our targets (targes) of war and our shields (escus) of peace. Whoever may choose to tilt with us has only to come, or send any one, the preceding day, to touch with a rod either of these shields, according to his courage. If he touch the target, he shall find an opponent ready on the morrow to engage him in a mortal combat with three courses with a lance : if the shield, he shall be tilted with a blunted lance; and if both shields are touched, he shall be accommodated with both sorts of combat." Here is a 15th c. illumination of Froissart, illustrating the jousts. A joust with sharp lances is shown: the illustrator has depicted the targe of war as concave with a notch for the lance, exactly what modern writers call an écranché shield, the other form hung from the tents is the older "heater" shape.
I should emphasize that in the context of the St. Inglevert, the “targe of war” was used for jousts with sharp lances and the “shield of peace” for jousts with blunt coronels. This did not necessarily mean that the targe of war was typical battlefield equipment.
The Gladiatoria fechtbuch also illustrates a small version of the écranché shield, and calls it a tartschen.
I don't wish to imply that all medieval writers were consistent and rigorous in using targe and shield to distinguish between the concave shield and the convex heater form. However, it is a convenient way to make the distinction that is consistent with period practice and uses English words.
It also allows us to recognize the significant category of jousting targes that were convex but without a cutout for the lance.
Although most often depicted as jousting equipment, the concave targe was also shown being used for single combat on foot, both in Gladiatoria and the Codex Wallerstein.
At least one illumination shows one being used in battle on foot, in BL Royal 20 C. VII. My line drawing of the scene is reproduced here on page 154.