It is a monohedral tiling: it consists only of one shape that tessellates the plane with congruent copies of itself. In this case, the prototile is an elongated irregular nonagon, or nine-sided figure. The most interesting feature of this polygon is the fact that two copies of it can fully enclose a third one. E.g., the lowest purple nonagon is enclosed by two yellow ones, all three of identical shape.[4] Before Voderberg’s discovery, mathematicians had questioned whether this could be possible.

https://en.wikipedia.org/wiki/Voderberg_tiling

Bonus tiling: