Set of which all seven elements are fittingly hidden in the solved puzzle grid

Question:

Answer:

TETRISPIECES

Length:

Similar Crossword Questions:

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
Theme of this puzzle, whose members are hidden throughout the grid
Award won by lead actors in this puzzle's starred films: the winners' names are hidden "word search"-style in the grid (across, down or diagonally, and forward or backward)
There are four hidden in this puzzle, which together suggest a familiar five-word saying (3,5,4,2,4)
Image this puzzle grid is supposed to suggest
"Inner voice" hidden in five puzzle answers
Their names are hidden in eight answers in this puzzle
Rap sheet letters hidden in this puzzle's longest answers
Historic symbol whose shape can be found hidden in this completed puzzle
Space-saving abbr. hidden in four puzzle answers
There are six hidden in this puzzle in appropriate places
Elite Navy group that's fittingly camouflaged in the four longest answers in this puzzle
Word hidden in this puzzle's theme entries
Hoop group hidden inside this puzzle's three longest answers
Featured article hidden in this puzzle's nine longest answers
Descriptive of this puzzle's grid
Last letter in most plurals (but not in this puzzle's six longest answers, which are the only plurals in this grid)
Business "meeting" hidden in nine puzzle answers
"Hidden" theme of the puzzle
Thing that may appear to be symmetrical but isn't ... like this puzzle's grid
Picnic serving, and when divided properly, a hint to a hidden feature of six pairs of puzzle answers
Entertainer (1938-2007) whose first name is hidden in eight puzzle answers including this one
List shortener hidden in eight long puzzle answers
Right now, as hidden in this puzzle's longest answers
Things hidden in this puzzle's eight longest answers