"Run out of" is a phrase used to describe a situation where a person or entity has completely used up a resource or item. For example, if someone says they have run out of milk, it means they no longer have any milk left in their refrigerator. This expression can apply to various items, such as food, supplies, or even time. In a broader context, "run out of" can also refer to exhausting options or opportunities. For instance, if a student runs out of time while taking a test, they may not be able to complete all the questions. This phrase highlights the limitation of resources in everyday life.