Semi-deciduous is a botanical term which refers to plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s that lose part of their foliage, also Semi-deciduous plants can mean, that plants can lose their foliage for a very short period, when old leaves fall off and new foliage growth is starting. This phenomenon

Phenomenon

A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

 occurs in tropical and sub-tropical wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

y species, for example in Mimosa

Mimosa

Mimosa is a genus of about 400 species of herbs and shrubs, in the subfamily Mimosoideae of the legume family Fabaceae. The generic name is derived from the Greek word μιμος , meaning "mimic."...

 bimucronata. Semi-deciduous may also describe some trees, bushes or plants that normally only lose part of their foliage in Autumn/Winter or dry season, but might lose all their leaves in a manner similar to deciduous

Deciduous

Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

trees in an especially cold Autumn/Winter or severe dry season (drought).