The phrase "horizontal row" refers to a line or a series of objects or elements that are arranged side by side in a flat or level position. Full definition
Many of these allow you to attack multiple enemies at once, or including all enemies in horizontal rows, vertical columns or 3 × 3 squares. (hardcoregaming101.net)
You can even do horizontal rows with the help of a stable table! (fitnessandpower.com)
You'll be starting this scarf in the center and working long horizontal rows upwards. (thespruce.com)