1. To briefly stop at and go into some location, especially to collect or purchase something. I just need to run in the office and get my phone charger. Do you mind if I run in and pick up some milk before we head home?

2. To bring someone to some location very quickly, especially by car. In this usage, a noun or pronoun can be used between "run" and "in." I just need to run Janet in to get her glasses fixed. I'll be home soon. A: "The tires are flat on my bicycle." B: "I can run you in, if you want a lift."

3. dated To bring someone to a police station after arresting them. In this usage, a noun or pronoun can be used between "run" and "in." The group of vigilante's ran in the suspected criminal so that he could be properly arrested by police. The cops ran him in to protect him from a hit by the Mafia.

4. To impale someone with a knife, sword, or other pointed weapon. The pirate ran the mutineer in with his sword. The mother of four ran in the burglar with a kitchen knife after discovering that her house had been broken into.

5. Of text in a book, to continue a paragraph without creating a line break of any kind. Quotes like this should only run in if they are two or three sentences long. This paragraph is way too long—it runs in for three full pages! I felt totally lost by the time I got to the end of it.