What does the cryptic crossword clue "Number of sheep, possibly, but not goats (8)" mean?

The definition is "Number of sheep, possibly, but not goats". The wordplay uses a cryptic definition. Cryptic definition The answer is SINGULAR.

Number of sheep, possibly, but not goats (8)

Times Cryptic #28667 | 1 Across | 2023-07-28 flower