A counterparty is obliged to lend or to borrow, on a future date, and at a rate defined today, a notional amount for a period of 1, 3, 6 or 12 months. The FRA is so defined by the forward staring time of the notional deposit and its maturity. A 1x4 FRA is a FRA on a deposit referenced to 3 months Euribor (4-1) starting in 1 month time.
Thus, the counterparty that buys the FRA is obliged to borrow a notional deposit. The FRA seller will then be obliged to lend the notional deposit. Both at the rate and date locked today.
Example:
The counterparty A buys a FRA by borrowing a deposit with a notional amount of €1,000,000 for 3 months, but instead of today, into 1 month time at a rate of 1%. Thus, counterparty B sells the FRA, and lends the notional amount of €1,000,000 for 3 months into 1 month time at the rate of 1%.