What does the idiom "an ace up one's sleeve" mean?

• The idiom "an ace up one's sleeve" means - To have a secret advantage or plan.

• an ace up one's sleeve (idiom)
English Meaning: a hidden strength or resource kept in reserve to be used when needed.
Bangla Meaning: গোপন কোনো শক্তি বা কৌশল যা প্রয়োজনে ব্যবহার করা হয়।

Example Sentence:
- He didn’t reveal his strategy during the meeting because he had an ace up his sleeve.

Source:
1. Cambridge Dictionary.
2. Accessible Dictionary by Bangla Academy.