A pace was an inexact measurement of distance, determined by the length of one walking step.
In 2368, Berlinghoff Rasmussen paced out Jean-Luc Picard's ready room from door to the window counting his paces in meters aloud "...four... five... six... seven meters," before laughing "HA! I was right!" All as a part of a ruse to convince the crew he was confirming information about them that he already knew. (TNG: "A Matter Of Time")
In 2372, Julian Bashir described Morn's inability to play darts by noting that he "couldn't hit a Yridian yak from 5 paces." (DS9: "Accession")