The long and short scales are two of several large-number naming systems for integer powers of ten, that use the same words with different meanings:

Long scale

Every new term greater than million is one million times larger than the previous term. Thus, billion means a million millions (10¹²), trillion means a million billions (10¹⁸), and so on.

Short scale

Every new term greater than million is one thousand times larger than the previous term. Thus, billion means a thousand millions (10⁹), trillion means a thousand billions (10¹²), and so on.