Conidia are asexually produced spores that are borne externally to the cells that produce them. This definition may be confusing, but it is only necessary to compare conidia with sporangiospores to see the difference. Sporangiospores are produced inside specialized cells called sporangia and remain enclosed in the cells until maturity. Conidia may be produced inside a cell although not always but at maturity they will be exposed to the external Asexual reproduction fungi conidia alternaria. There is some grey area here but for the most part our definition will hold up.
Asexual reproduction by conidia is a major part of many fungal life histories. The conidia of these fungi not only germinate and produce a new generation, they also function in dispersal and so have physical characteristics suited to the most efficient performance of this role.
Fungi occur in a large variety of habitats and have an equally large variety of dispersal mechanisms, including conidial form. The pictures shown above may give you some idea of just how diverse these forms can be. Conidial fungi are ubiquitous in nature and in human environments.