X is a surface with only one side and one boundary component.
The Euler characteristic of X is zero.
X has a mathematical property of being non-orientable.
A line drawn on X, starting from the seam down the middle will meet back at the seam but at the “other side”. If continued the line will meet the starting point and will be double the length of the original strip
Identify X which was discovered independently by the German mathematicians August Ferdinand ‘X’ and Johann Benedict Listing in 1858 and considered as a mathematical ingenuity.