A stroop is the smallest amount of the lumen that the Stellar network can record, equal to 0.0000001 lumens, or one ten-millionth of one Stellar lumen (XLM). Stellar's software stores all balances and fees internally as whole numbers of stroops, which avoids rounding errors, and amounts are displayed in lumens for users. The unit appears most often in discussions of transaction costs: the network's minimum base fee is 100 stroops per operation, a tiny fraction of a cent, which helps Stellar market itself for low-cost payments and remittances. Stroops play the same role for Stellar that satoshis play for bitcoin, wei for ether and the lovelace for Cardano's ADA, letting very small values be counted precisely.