The noun 'trio' can function as a collective noun for any group of three joined together on a common task:

• a trio of singers
• a trio of dancers
• a trio of waiters
• a trio of EMTs
• a trio of horses
• a trio of elephants

A trio means three (of people, of things, of events). Examples:

1. A trio of singers performed.
2. I saw a trio of stars above the pines.
3. A trio of baby rabbits sat in my yard.
4. Though I already won twice, I wanted a trio of wins.
5. Three makes a trio of anything.
6. A trio of blue birds ate from the feeder.