The process whose specific outcome is the progression of conidium over time, from its formation to the mature structure. Conidia are non-motile spores produced via mitotic asexual reproduction in higher fungi; they are haploid cells genetically identical to their haploid parent. They are produced by conversion of hyphal elements, or are borne on sporogenous cells on or within specialized structures termed conidiophores, and participate in dispersal of the fungus.