1. To provide information or details, usually by actually writing something in a blank space on a test, form, etc. Fill in the blank with what you think is the correct answer.

2. To figure something out; to determine an answer to something that was previously unknown. My parents may not know who dented the car now, but they'll fill in the blank eventually.

1. verb Literally, to complete a statement by adding information to a space that has been intentionally left empty or blank. The instructions at the top of the test sheet told us to fill in the blanks with the correct information about World War I.

2. expression A phrase used when one does not supply all the necessary information, instead relying on the listener to infer the missing details. A: "What happened last night between Katie and Rob? I saw them leave the bar together." B: "What do you think happened? She went home with him—fill in the blanks!"