Answer:
An unique characteristic of the Earth is that our planet is located in a specific area of the solar system where water can easily be found in liquid form.
And even if Earth is not the only celestial body of the solar system where water can be liquid, it is the place with the highest amount of liquid water in proportion to its total mass.
The importance of this characteristic is that water is a very important source for life because it is the best chemical solvent, meaning that molecules can easily form, merge, and break up, inside a water solution.