What shape has fewer than 3 vertices?

Answer 1

There are many shapes that have fewer than 3 vertices like the circle, hyperbola, semi circle, and many others.

However if you are only talking about polygons then there is no actual shape with fewer than 3 vertices that you can find in a real life situation but they do have names for these shapes. A 2-sided polygon is known as a digon. A 1-sided polygon is known as a monogon. These shapes only exist in theory however and not in real life.