What is defined as a plant growing where it is not wanted?

A weed is defined as a plant that grows in an undesired location, often competing with cultivated plants for resources such as water, nutrients, and light. Weeds can be invasive and can disrupt the balance of an ecosystem, affecting agricultural productivity and the health of native plants. The term "weed" applies to a wide variety of plant species that may not have intrinsic negative traits but are considered problematic due to their growth habits in a given context.

Flowers, grass, and shrubs do not carry the same connotation. Flowers may be cultivated for beauty or specific purposes, grass can be purposeful in lawns and pastures, and shrubs typically serve ornamental or functional roles in landscaping. Thus, their classification does not align with the definition of unwanted growth characteristic of weeds.