row
A row is one horizontal line of a matrix — the numbers you read straight across, left to right, like reading a line of text. If a matrix were a stack of trays, each row would be one tray laid out flat.
Rows are numbered from the top down: the first row is the topmost line, the second row is the one below it, and so on. A matrix with m rows has m of these horizontal lines stacked on top of each other.
Rows matter because so many matrix techniques act on whole rows at a time. Solving a linear system, for instance, is largely a story of shuffling and combining the rows of a matrix until the answer appears.
Reminder: the English word “row” is the horizontal one. In Chinese this is 行 (Simplified) / 列 (Traditional, as used here). Confusing rows with columns is the single most common matrix mistake for beginners.