Crossword puzzle clue "they come three rows to a package"

One who rows, rows, rows the boat

They come three rows to a package

Web concerns ... and based on six familiar names hidden in rows 1, 4, 12 and 15 of this puzzle grid, what the black squares in those rows symbolize

Rows of rows

One way of ordering things, like all the consonants in rows three, six and nine

MD (a pair of which are found in three rows of this puzzle)

Rows of three or more stamps: Philately.

Vessels with three rows of oars