Harsh climates or conditions are very difficult for people, animals, and plants to live in.

Harsh actions or speech are unkind and show no understanding or sympathy.

Something that is harsh is so hard, bright, or rough that it seems unpleasant or harmful.

Harsh voices and sounds are ones that are rough and unpleasant to listen to.

If you talk about harsh realities or facts, or the harsh truth, you are emphasizing that they are true or real, although they are unpleasant and people try to avoid thinking about them.