A houseplant
is a plant that is grown indoors in places such
as residences and offices, namely for decorative purposes,
but studies have also shown them to have positive psychological
effects. They also help with indoor air purification, since
some species, and the soil-dwelling microbes associated with
them, reduce indoor air pollution by absorbing volatile organic
compounds including benzene, formaldehyde, and trichloroethylene.
While generally toxic to humans, such pollutants are absorbed
by the plant and its soil-dwelling microbes without harm.
More info at wikipedia