The word "fern" refers to a group of vascular plants that reproduce via spores - i.e. they do not produce seeds, fruit, or flowers. You were probably introduced to them as a child, when an adult, friend, or science teacher turned over a fern leaf to show you the tiny dots on the leaf's underside that make up the unique plants' reproductive system.
First appearing on the fossil record 360 million years ago, ferns are one of the oldest species with which we share this current time on earth. The "interrupted fern," Osmunda Claytoniana, is believed to have remained unchanged for the past 180 million years.
Used in some medicinal recipes and cultivated as ornamentals, ferns are also used to remediate contaminated soil. Though not a huge commerically-used plant, ferns have remained an important ally to the human species because of their beauty and ability to remove chemical pollutants from the air and soil.