A yabby is a small crayfish that is found in creeks, rivers and billabongs in Australia. They can be caught and eaten in much the same way as larger crayfish.

Photo by Ioan Sameli

A yacht is a type of fast sailing boat. Sailboats do not have engines or motors, they move because the wind blows them along.

Photo by Gainesmary28

A yak is a relative of the cow. Yaks live in high mountains, and have long shaggy hair to keep out the cold.

Photo by Deadrobot

Scientific name: genus dioscorea

A yam is the tuber of a vine, found in many countries around the world. Yam tubers can grow very big - up to 70kg. Yams have a rough skin that is hard to peel, but much softer flesh inside.

Some variety of yam can be eaten raw, but most need to be cooked. Yams can be fried, boiled, pounded down and made into a dough, or something similar to instant mashed potato made from dried, powdered yam.

Many people call sweet potatoes yams or sweet yams, but they are actually different vegetables.

A wikimedia image

Yarn is made from animal hair, spun into a long, thin, string. It can be made in any thickness and then dyed in any color. People then use the yarn to knit things like socks out of.

Photo by LollyKnit

A yawn is where your mouth opens wide and you take a deep breath in and out. Yawns just happen by themselves, they are hard to stop.

People and animals yawn when they are tired, stressed, overworked or bored, or for no reason at all. Yawning is infectious - if someone near you yawns, you often start yawning too! You might even start to yawn by looking at a photo of someone yawning, so don't stare at the photo of the yawning cat for too long.

Photo by Kaibara87

Yeast is a very tiny fungal organism. Some species of yeast are used in baking and brewing. Yeast can make bread rise and become light and fluffy, and it can be used to make some wines and beers.

Yeast extract is used to make some very strongly flavoured spreads like Vegemite.

Photo by Sierravalleygirl

Yellow is a very bright colour often seen on insects, fruits and flowers. It is a primary colour, which means yellow paint can be used to make other colours but you can't use any other colours to make yellow paint. The bird in the picture is yellow.

Photo by Tanakawho

A yoyo is a toy made from two heavy halves with a gap between them. A string is looped around an axle in the gap, but not tied on. You hold onto the end of the string, usually by a loop that goes around your finger, and you can make the yoyo go up and down. You can also do lots of other tricks once you get good at playing with a yoyo.

Photo by Adriano Agulló

Yoga is a traditional mental and physical discipline originally from India. In modern times in the Western world, yoga usually takes the form of poses and stretches as a form of exercise, but traditionally was also an aid to meditation.

Photo by Judepics