The creation of new plants from existing ones, either sexually (from seed) or vegetatively (from cuttings, division, layering, or grafting).
Propagation is plant multiplication. Sexual propagation (seed) creates genetically different offspring; vegetative propagation (cuttings, division, etc.) creates identical clones. Each method has pros and cons. Seed is cheapest but slowest and produces variable plants. Cuttings and division are faster and true-to-type but more labor-intensive.
Understanding propagation methods lets you multiply favorite plants for free or start with cost-effective seed instead of buying plants.