Crossword puzzle clue "rows of three or more stamps philately"

Rows of three or more stamps: Philately.

One who rows, rows, rows the boat

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

Prefix for philately

Practiced philately

Philately offering

Philately collection