Unique is an adjective meaning being the only one of its kind; unlike anything else.
In mathematics, unique refers to a solution that is the only one possible.
The term "unique" can also be used in these contexts:
1. Unique identifier - a number or code assigned to identify one unique entity
2. Unique selling point (USP) - what makes a product or service stand out
3. Unique visitor - in web analytics, an individual user