Once or twice
Definition 1 of 1
Pro Tip 1/3Not regularly
Used when an action is done infrequently, emphasizing it's not a habit or common occurrence. 
I go to the cinema once or twice a year.
Pro Tip 2/3Conversation Softener
It downplays frequency to seem modest or casual, often when you're more familiar than you want to admit. 
I've met him once or twice, though we've actually had many meetings.
Pro Tip 3/3Potential Understatement
The phrase may be an understatement, especially in modest or polite contexts. 
I've read his work once or twice.