depends on what you mean by the question.
it is a whole
next to 0, it is the easiest thing to multiply by
it is the first ordinal number
it is an Arabic numeral
it is the first of the natural numbers
it is the second of the base ten numbers
it is the integral ( -infinity to infinity) of f(t)\ dt
in real numbers it the infinitely recurring decimals 0.99999999... and 1.000000... .