What is the term for a plant that has a soft, nonwoody stem that typically dies down at the end of each growing season?

A plant with a soft, nonwoody stem that typically dies down at the end of each growing season is known as an herbaceous plant. This classification includes a wide variety of plants that possess flexible stems and often die back to the ground during the winter months, reemerging in the spring with new growth. Common examples of herbaceous plants include many flowers, vegetables, and ornamental garden plants.

In contrast, a deciduous plant is one that sheds its leaves annually but may still have a woody structure, while a woody plant refers specifically to those that have a more rigid and persistent stem structure, such as trees and shrubs. Perennial plants are those that can live for more than two years, which may include both herbaceous and woody types. However, the defining characteristic of an herbaceous plant is precisely its nonwoody stem and seasonal decay. Thus, it is the right term to describe plants that demonstrate the given characteristics in the question.