All types of plants were originally outdoor plants, of course, but certain plants are now referred to as indoor plants, or houseplants, because of their low tolerance for cool temperatures, their long life span, and their ability to thrive in containers. Most outdoor plants have dramatically visible signs of death or dormancy. Plants wither, lose leaves and decay. Annual plants only last for one growing season, and perennial plants return after a period of dormancy. Indoor plants also have a dormant period. Indoor plants will stop growing during autumn and winter; some plants may look faded and tired during their dormant period.