also: ぜんにっぽん
all of Japan; the whole of Japan
Refers to Japan as a whole, often in somewhat formal, journalistic, or emphatic wording; 日本全国 is the more everyday way to say 'throughout Japan.'
All of Japan paid attention to the news.
all-Japan; national; Japan-wide
Prefix-like use in names of competitions, organizations, surveys, and similar nationwide things. The compound after 全日本 determines the exact meaning.
He competed in the All-Japan Championships.
All-Japan Championships; Japanese national championships
Abbreviation for a national championship event, especially in sports or competitions; the specific sport is understood from context.
She won this year's national championships.
Japan national team
Abbreviation for the Japanese national team, mainly in sports contexts; often used in expressions such as 全日本に選ばれる.
He was selected for the Japan national team at the age of twenty.
The All-Japan Table Tennis Championships will be held next month.
He was selected for the Japan national team while he was in high school.