Language revival is people trying to make a language spoken often again when it is not spoken or is spoken very little. Language death happens when a language is not used by the people who used to speak it.
Language revival tries to save a language that is dead or endangered. The Hebrew language was once a language that was not spoken, but the language was revived, and people now speak and use it again. Many people are now trying to revive their languages. The revival of languages is useful as it can give insight to older languages.