Mildot
An older mil-based reticle with circular dots at 1-mil intervals along the crosshair. Largely superseded by Christmas-tree and grid reticles.
The mildot pattern was the precision-rifle standard for decades. It was simple, easy to learn, and sufficient for hold-over and range estimation against known target sizes. Each dot subtends 0.2 mil; dot-to-dot is 1.0 mil.
Modern reticles (Horus, Tremor, EBR, MSR) replace mildots with denser grid patterns that include hold-off windage marks. Still, “read X mils on the reticle” remains the way most precision shooters describe holds.