The most common and most likely answer to this crossword clue is the 8 letter word QUARTETS
I've seen this crossword clue in The Guardian
Q
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Buddy explains!
The straight part
We know that "Groups of 4" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case groups of 4 = quartets.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does QUARTETS mean?
QUARTETS noun- A music composition in four parts, each performed by a single voice or instrument.
- The set of four musicians who perform a piece of music together in four parts.
- A group of four singers, usually males, who sings together in four-part harmony.
- Any group of four, especially people.