Prayer flags are cloth objects with prayers printed on them used by Himalayan Buddhists, in a manner similar in idea to the prayer wheel. The prayers are "read" as the flags flap in the breeze.
Prayer flags are printed using a woodcut, about 1 x 1 foot (30 x 30 cm.) on long bolts of fabric, one pane wide. The prayer is printed in black on five different colors of fabric, for each of the five elements: white - air; blue - water; red - fire; green - wood; and yellow for earth.
The flags are erected in significant places - near homes, at mountain passes, or white flags in areas where the dead are mourned. They are generally attached to tall wood poles, the selvedge side of the fabric attached to the pole, so that the flag will gradually blow away into the wind. When the flag wears out, it is replaced.
It is improper to pick up a prayer flag that has fallen to the ground, thus in areas where there are many prayer flags, one may often see many on the ground. These are often somewhat wooded, not areas where people might walk on them. The flags are made of a relatively lightweight, cheap material, that decays relatively rapidly once it has fallen - within a year or two. It is also appropriate, in certain circumstances, to burn the flags.
It is considered bad luck to buy an even number of flags at one time.