Frozen is the past participle of freeze.
2. adjective
If the ground is frozen it has become very hard because the weather is very cold. ■ EG: ⇒ It was bitterly cold now and the ground was frozen hard. ■ EG: ⇒ ...the frozen bleakness of the Far North.
3. adjective
Frozen food has been preserved by being kept at a very low temperature. ■ EG: ⇒ ...frozen desserts like ice cream.
4. adjective
If you say that you are frozen, or a part of your body is frozen, you are emphasizing that you feel very cold. (emphasis) ■ EG: ⇒ He put one hand up to his frozen face.
phrase
Frozen stiff means the same as frozen. ■ EG: ⇒ It was cold and damp; he pulled up his collar and was aware of being frozen stiff.