1 lot for currencies means 100 000 units of base currency.
Example: Let's say now GBPUSD 1.55 (1 pound=1.55 USD). You buy 1 lot GBPUSD. That means you buy 100 000 pounds and sell 155 000 USD.
1 lot for Gold means 100 ounce
1 lot for Silver 5000 ounce
