They are microscopic organisms which reproduce both sexually and asexually. Oomycetes are some of the most notorious pathogens of plants, causing devastating diseases such as potato blight and sudden oak death.
They are often referred to as water moulds (or moulds), although the water-loving nature which led to that name is not true of most species, which are terrestrial pathogens.
Images for kids
Oomycete Facts for Kids. Kiddle Encyclopedia.