A ponnuki is the process of capturing a single stone, leaving a diamond shape. Some people refer to it as a flower, as in the Chinese term.
This move and its resulting shape, radiating influence in all directions, is considered a very good one, as is witnessed by the proverb "A ponnuki is worth thirty points". We cannot take the number of points literally, OC.
That does depend on the positions of other friendly black stones: a good ponnuki is under-concentrated, not overconcentrated. Some people, such as Guo Juan in her online school, prefer to reserve the term ponnuki for cases where the shape is indeed powerful.
 See her Terminology lecture 2 at https://internetgoschool.com/auth/lectures/1794.lecture?, at time 06:10.