The mood used to express wishes, hypothetical situations, or indirect speech.
German has two types of subjunctive: Konjunktiv I (used primarily for indirect speech) and Konjunktiv II (used for wishes, hypotheticals, or polite requests).
Examples
Konjunktiv I:
Er sagt, er habe keine Zeit.
He says he has no time.
Konjunktiv II:
Wenn ich mehr Zeit hätte, würde ich reisen.
If I had more time, I would travel.
Ich wünschte, es wäre Sommer.
I wish it were summer.