A flat board usually covered with an ironing board cover on which clothes are laid while being ironed.

To keep the clothes flat while the the wrinkles are ironed out. Try ironing on a bumpy surface and you'll be praising the ironing board.

Ironing boards (as far as I've seen) are usually shaped like a stubby crayon. The pointy end works out nicely for shirt sleeves and pant legs.

I've seen 3 major types of ironing board. Short-legged boards for table tops or counter tops. Long-legged boards for standing on the floor. And ironing boards that fold out of a closet or down from the wall. I've only seen this last type in comedies and cartoons, but they seem to be quite dangerous.

Here's my ASCII interpretation of a long-legged ironing board:
 /'              |
(                |
    \\. //\\ .// 
 m1a `\\.  .//.  
    // `\\//  \\ 
   ||  .//\\.  ||
   ||.//   `\\.||
   |//       `\\|
   ''          ``