A herbicide is a type of chemical substance specifically designed to control, suppress, or eliminate unwanted plants (commonly known as weeds) that compete with crops, lawns, or other desirable vegetation. These chemicals disrupt the growth processes of weeds by targeting essential functions such as photosynthesis, protein synthesis, or cell division. Herbicides can be selective, affecting only certain plant species (like broadleaf weeds in cereal crops), or non-selective, which kill nearly all vegetation they come into contact with.

They play a vital role in modern agriculture, landscaping, and forestry by reducing manual labor, improving crop yields, and maintaining soil health. However, responsible use is critical, as excessive or improper application can lead to environmental impacts, such as soil degradation, water contamination, or harm to non-target plants and wildlife.