a hundred: the cardinal number 100
This is simply the Hebrew word for the number one hundred. Most of its appearances are plain arithmetic: the years of a person's life (Abraham fathered Isaac at a hundred), the size of an army or a herd, sums of money and weights of metal, and the running totals in the long census and genealogy lists. When the Hebrew counts above one hundred it stacks the words together, so the same word also turns up inside larger figures such as two hundred and six hundred.
A few times the number is used to picture a large amount rather than to count exactly. When Isaac reaps a hundredfold harvest, or when five people are said to chase a hundred and a hundred to chase ten thousand, a hundred stands for an impressively big result. This is still the ordinary number doing ordinary work; the writers simply chose a round, sizeable figure to make their point, much as English speakers say a hundred times to mean very many times.
There is no hidden second meaning to hunt for here. Whether it is counting heads, marking an age, or painting a vivid contrast, the word means one hundred throughout.