Oospores are specialized sexual reproductive cells of some organisms, especially of fungi and algae. These cells are characterized by thick walls and can persist in unfavorable conditions for long periods. Synonyms for oospores include resting spores, thick-walled sporangia, zygospores, and sexual spores. Resting spores are common in many pathogens and are produced to survive the harsh environments during winters. Thick-walled sporangia are produced in some fungi, especially in plant pathogens, and can survive in soil for several years. Zygospores are sexual spores produced in some fungi and algae, where the cells undergo a complex sexual reproduction process. Lastly, sexual spores are formed through sexual reproduction and are an important mechanism for genetic recombination in various organisms.