This pattern expresses hesitation.

- Is used with action verbs and 있다/to have or exist
- when used as a sentence ending, it's used as a question/interrogative
- when used as a connective between two clauses, it's usually followed by -다가, 망설이다/to hestitate, or 생각 중이다/in the middle of thinking
- instead of 말까, other verbs can be substituted

Examples:
도망갈까 말까 하다가, 그만두었어요./I hestitated whether to run away or not, but I didn't.
효리를 도와 줄까 말까?/Should I help Hyolee or not?
편지를 쓸까 숙제를 할까 하다가 아무 것도 못했어요./I hestitated to write a letter or do my homework and ended up do nothing.