This is the 448th most frequent Hungarian word.
külső
"Outer," "external," or "exterior."
Here, 'külső' modifies 'tükör' (mirror), referring to the one located outside of the car.
Az autóm külső tükörjét megkarcolta valaki.
Someone scratched the external mirror of my car.
In this sentence, 'külső' is used as an adjective to describe the external or outer part of something, in this case, the house.
A ház külső része frissen lett festve.
The exterior part of the house has been freshly painted.
In this instance, 'külső' is used as a noun implying external or surface features, like appearance.