What does it mean to fill somebody in?

To fill somebody in means to give someone information that they are missing, to update them on what has happened, or to provide details to bring them up to date on a situation they were not present for. For example, if a coworker missed a meeting, you might fill them in on what was discussed, decisions made, and next steps. It implies sharing relevant facts, context, or background so the person can understand and participate fully. The phrase is commonly used in workplace, social, and everyday conversations as a friendly way of keeping someone informed. It can also be used when you need to provide more complete information after a brief explanation, like let me fill you in on the details. The expression suggests you are filling a gap in someone's knowledge, similar to filling in blanks. It is generally neutral and helpful, not secretive, and is often used as fill me in when asking for an update. It is a phrasal verb that functions as an informal but professional way to ensure shared understanding.