Several brokers, particularly those built for smaller accounts, drop lots entirely and let you enter 3,700 units of EUR/USD. One lot is simply 100,000 units, so 0.037 lots and 3,700 units are the same position.
Units make position-sizing arithmetic direct: choose the dollars you are willing to lose, divide by the stop distance in price terms, and you have the unit count. No rounding to the nearest micro lot required.
Example: risking $150 on EUR/USD with a stop 62 pips away. 62 pips is 0.0062 in price. Units = 150 / 0.0062 = 24,193. That is 0.24 lots, which a lot-based platform would round to 0.24 and a unit-based one would take exactly.
Related: nano-lot, lot-size-calculation, pip-value, standard-lot