Araignée is the traditional name in France. Elsewhere, butchers sell the same piece — or a close cousin — under a different name.
Third member of the *morceaux du boucher* trio — all three (poire / merlan / araignée) are French-butchery boucher's-secret cuts traditionally kept by the butcher.
Both *morceaux du boucher* — small premium muscles on the round, traditionally kept by French butchers. Araignée is the spider-shaped muscle on the rear thigh; poire is the pear-shaped muscle on the inside thigh. Different muscles, same cultural-identity category.