2 is a prime number and is the only even prime number.

= 1 x 2
Factorial 2 or 2!

1, 1, 2, 3, 5, 8, 13…
A Fibonacci number.

A deuce, a couple, a brace, a duo or a pair…

There are two blades on a pair of scissors and two sides to a piece of paper. People have two hands and so do some clocks. There are two sexes and two sides to an argument. Two-dimensional means that something has just length and width, but no depth.

Two’s company, three’s a crowd all depends on who you happen to be with.

Bi- means two. For example, a bicycle has two wheels and a bigamist has two husbands or two wives.