Cornsilk is a collective noun for the threads that envelope the top half of an ear of corn, lying between the kernels and the husks. It is fine and soft, quite like the silk it has been named for. When fresh, cornsilk is light green or yellow in colour; it darkens when dry.
I never liked cornsilk: it's perversely difficult to dispose of (it sticks to fingers and kernels like crazed weasels). Turns out cornsilk threads are the stigmas from the female flowers of corn (maize), so they obviously have a reproductive function, and it turns out they are thought to have medicinal uses as well. Cornsilk is apparently a "soothing diuretic" and is used by French herbalists to thin the bile and promote bile flow. Well, so says http://www.purplesage.org.uk/profiles/cornsilk.htm, anyway. But I like my bile just the way it is, thanks very much, so I'm going to continue to rip cornsilk out and toss it away, just as I always have.
Cornsilk is also an HTML colour (#FFF8DC); it's rather bland, so I think I'll just avoid the whole cornsilk thing altogether when I can.