11 (number)

natural number

In geometry, a hendecagon (also undecagon or endecagon) or 11-gon is an eleven-sided polygon. (The name hendecagon, from Greek hendeka "eleven" and –gon "corner", is often preferred to the hybrid undecagon, whose first part is formed from Latin undecim "eleven".)

Undecimal (also known as unodecimal, undenary, and the base 11 numeral system) is a positional numeral system that uses eleven as its base. While no known society counts by elevens, two are purported to have done so: the Māori (one of the two Polynesian peoples of New Zealand) and the Pañgwa (a Bantu-speaking people of Tanzania). The idea of counting by elevens remains of interest for its relation to a traditional method of tally-counting practiced in Polynesia.

In geometry, a hendecagram (also endecagram or endekagram) is a star polygon that has eleven vertices.

Ulster Protestant celebration in Northern Ireland