Pip

The standard smallest price increment for a currency pair, usually 0.0001 for most pairs.

Example

EUR/USD moving from 1.1000 to 1.1010 is a 10-pip move; on a 100,000-unit lot that is 100 dollars.

Moves of a few pips sound tiny, but with leverage they can be a large share of a trader's margin.

Lot Size — The quantity of currency in a trade; a standard lot is 100,000 units of the base currency.
Currency Pair — Two currencies quoted against each other, showing how much of the second is needed to buy one unit of the first.

Every currency trade is a bet on two countries at once — A forex position is always one currency against another. Retail traders usually hold it through leveraged broker products, while every international investor already holds currency risk without trading at all. (9 min)
Price moves, interest differences and leverage - in a market where one side's gain is the other's loss — Forex returns come from exchange-rate moves and interest-rate differences, magnified by leverage, in a market that is roughly zero-sum before costs and negative-sum after them. (12 min)
Appraising one trade: size it from the loss, not from the leverage — Before a currency trade, set how much of your account you will risk, where the trade is wrong, and what the broker and costs add. Position size follows from those, never from the maximum leverage available. (12 min)