Unicellular organisms reproduce asexually by the process of binary fission or budding. In binary fission, the organisms divide into two organisms by single division of the cell. In budding, a bud appears on the cell; grow for a while and then detaches to form a new organism.
Budding in Multicellular organisms: In Hydra, a bud develops as an outgrowth due to repeated cell division at a specific site. Each such bud develops into a tiny individual hydra.