What is the definition of "expel" in a medical context?

In a medical context, "expel" refers to the process of pushing out waste or unwanted substances from the body. This term is often used in relation to bodily functions, such as the excretion of waste products through urine or feces, or the expulsion of mucus or fluids during a respiratory illness. The focus on the mechanism of removal underlines the body's need to eliminate materials that are no longer useful or could be harmful if retained.

The other definitions do not align with the medical understanding of "expel." Decreasing in size does not pertain to the act of removal, outlining a shape is more related to visual representation or diagramming, and measuring depth pertains to determining the extent or dimension of a particular material or space, which again is not relevant to the concept of expulsion within a medical framework. Therefore, the correct answer accurately captures the essence of the term in healthcare contexts.