"A stem is a part of the plant that is a central shoot that holds the leaves, branches, flowers, and so on.  The true rhubarb stem is a hollow, nearly bamboo-like cylinder, which leads up to a terminal shoot that eventually develops flower buds. A stalk, on the other hand, can be both leaf stalk and the stem of a plant."

Stalk :- The slender attachment or support of a leaf, flower, or fruit. It's also called petiole... It is that part of flowers or leaves where we hold them... For example, ‘the acorns grow on stalks’ Stem :- The main body or stalk of a plant or shrub, typically rising above ground... Or A stem is a part of the plant that is a central shoot that holds the leaves, branches, flowers, and so on.

Stem- when someone gives you a flower, it's where he or she holds it. Stalk- the whole body of the plant. When you see farmers harvesting rice or wheat, they're actually pulling the stalk out of the ground.