While Gordon Moore's paper originally stated that Moore's Law meant a doubling of transistor density roughly every two years, and some suggest a doubling every two and a half years, the managerial definition of Moore's Law that you'll often see appearing in the trade press is:

Chip performance per dollar doubles every 18 months

Explanation:

This law says that the number of transistors that can be fit on a computer chip will double every 18 months resulting in periodic increases In computing power.

This is more often seen appearing in the trade press because that law is being used as the basis to push their market.