Yardang - a ridge of rock in an arid area which is aligned to the prevailing wind direction. Small examples may only be a metre high but larger ones can be dozens of metres above the level of the trenches between them

Yield - the amount produced. In agriculture it is usually a measure of the tones of useable produce per unit area.

Younger-Dryas - a cold period of about 1500 years that occurred at about 10,000 to 8,500 years ago. Thought to have been brought on by a sudden release of cold water into the oceans from behind the North American ice sheets which were breaking up at about that time.