行 (háng) as a noun means 'row, line' (e.g., a row of seats) or 'trade, profession' (e.g., 行业). As a classifier, it counts rows or lines of things. Compare 排 (pái) — 排 is also a classifier for rows, but 行 emphasizes the line itself (like a line of text), while 排 focuses on the act of arranging or the resulting row (like a row of people).