What does the cryptic crossword clue "Pose with ten performing old dance (3-4)" mean?

The definition is "dance". The wordplay uses an anagram. anagram of POSE + TEN = ONE-STEP; definition: "dance" The answer is One-step.

Pose with ten performing old dance (3-4)

Telegraph Prize Cryptic #3037 | 9 Across | 2020-01-05 flower