Recto is the "right" or "front" side and verso is the "left" or "back" side when text is written or printed on a leaf of paper in a bound item such as a codex, book, broadsheet, or pamphlet.
Grandes Heures of Anne of Brittany, f. 189v-190r
Hypatian Codex, folio 3 verso, pencil-marked "3 об" in the top left corner. At Izbornyk, this is written as "/л.3об./".