Fenestration is a term in botany that refers to natural holes in the leaves of some species of plants. The size, shape, and quantity of holes in each leaf can vary greatly depending on the species and can even vary greatly within a given species. Fenestration is caused by sections of leaf ceasing cell growth or by dying during an early stage in the development of the leaf. These deformations that are created earliest in the leaf development end up looking more like slashes whereas those that develop earlier end up looking more like holes. This trait is found in only one species in Aponogetonaceae and a few genera in Araceae.
Its not fully known what evolutionary purpose fenestration serves, but there are several possibilities. Fenestration could serve the purpose of reducing the chances of leaves tearing in high winds or it could help to maximize the amount of rain that's able to reach the plant's roots. Another possibility is that they help to cool the plant by producing turbulence around the leaf.
The term is also used to describe plants with holes in their trunks, such as Platypodium elegans which can be mistaken for a strangler fig.[1]