The term 'UNLESS' is a conjunction that is used to introduce a condition or exception. It is often used in the same way as 'except when' and can be used interchangeably. The word 'UNLESS' is six letters long and is used to indicate that something will not happen UNLESS a certain condition is met. For example, 'I will not go outside UNLESS it is sunny.' In this sentence, the speaker is indicating that they will not go outside UNLESS the weather is sunny.