All season tyres are tyres that, as the name suggests, have a tread pattern suitable for use all year round. They have a tread pattern that is more heavily siped than a summer pattern but not as heavily siped as an out and out winter tyre.
They will provide perfectly adequate performance in summer conditions and usually have a small amount of winter driving ability. They allow for the use of the same tyres all year round, negating the need for changing from summer to winter tyres. They are not so popular in the UK, where a summer tyre is generally used all year round.
Below is a selection of all season tyres available, showing different tread patterns: