In the USA, as albums reach certain sales levels, the RIAA (Recording Industry Association of America) awards them Gold or Platinum status.
Gold represents 500,000 copies sold, Platinum represents 1,000,000, and Multi-Platinum represents (duh) multiples of 1,000,000.
Below is a list of just how much precious metal Tool has been awarded so far in the USA, including certification dates - which is not the actual date the sales mark was reached.
You can check certification data for other artists in the RIAA's online database. §