What is stalk? What is stalk? A stem or main axis of a herbaceous plant.A stem or similar structure that supports a plant part such as a flower, flower cluster, or leaf.A slender or elongated support or structure, as one that holds up an organ or another body part.To walk with a stiff, haughty, or angry gait: stalked off in a huff. To move threateningly or menacingly.To track prey or quarry.To pursue by tracking stealthily.To follow or observe (a person) persistently, especially out of obsession or derangement.To go through (an area) in pursuit of prey or quarry.