頑張れ

Etymology
The of verb.

The kanji spelling is an example of ateji (当て字)

Verb

 * 1)  do your best, good luck, hang in there, come on, don't give up, keep going

Usage notes
Used for encouragement or cheering on (where English "good luck" is often used), its actual meaning is closer to "do your best" or "give it your best". As a phrase, it does not contain any reference to luck, but rather effort and hard work. Compare French.

As the strong imperative form, it may be considered rude if used directly to a single person. Consequently, this term is more often used when cheering on a team or group. To encourage a single person, the conjunctive (weaker imperative) form is more common.