The phrase "run down" has several meanings, depending on its context.
1) In a general sense, it can refer to something that is in poor condition due to wear and tear or neglect - for example, "the building was run-down".
2) It can also be used figuratively to describe someone who is exhausted or fatigued - as in, "I feel so run down today."
3) In a more specific sense, it can refer to the act of gradually reducing something over time. For example, "we need to run down our inventory before we place new orders".
4) Finally, it can also be used to describe someone who is talking excessively or at length - as in, "he just keeps running down his opponent."