A "pip" (percentage in point) is the smallest standardized price move for most currency pairs, typically the fourth decimal place (0.0001) for pairs quoted to four decimals, and the second decimal place (0.01) for JPY pairs.
Pip value depends on the pair, the lot size, and the account currency. For a standard lot (100,000 units) of EUR/USD, one pip is worth roughly $10. For a mini lot (10,000 units), it is roughly $1. When USD is the quote currency, pip value is fixed; when it is the base currency, pip value fluctuates with the exchange rate.
Traders use pip value to size positions against a fixed risk budget: divide the dollar amount you are willing to lose by the stop-loss distance in pips to get position size. Getting this calculation wrong is one of the most common reasons new traders blow up small accounts.