Direct translation is "10000 years!". Thus, it can be applied not only to emperors but to anybody anything.
The word was invented about a hundred years ago in the period of Meiji emperor era, the era when Japan opened to the world and rapidly modernized and defeated China and Russia at wars.
Ever since the word is commonly used by Japanese peopele when some good fortune occured to them in private life to official matters. Nowadays the word is nothing to do with emperors.
To Americans, banzai became familiar with the scenes of Japanese soldiers shouting when they won battles or when they committed suicidal and kamikaze attakcs. As old Japanese society never allowed Japanese to surrender, they had no choices but die, and the last moment they shout "banzai".
When accepted by a great University, a student would say "Banzai".
Where when the enemy has weakened their unit to the point where it has no option but to retreat or surrender, they issue a "Banzai" charge in which they rush head first into the enemy and attempt to engage in close combat, usually with bayonets and swords.
Typically an act of self sacrifice rather then to dishonor their army and country by surrendering to the enemy, an action related to Bushido.
It is traditional to scream the word before attacking followed by a non-linguistic war cry.
2. Slang in video games for a hopeless rush against the enemy, often without any Japanese or Bushido affiliation.
"Shit, banzai charge! Fire at will!"
2. Damn man you banzai'd bad on that one.
2. A moderately funny TV show on Channel 4 UK TV. Uses sounds and music from the famous Bruce Lee film, Enter The Dragon.
Mister Cheeky Chappy very happy!
You phone up the person in question with an unknown number
they answer: ''Hello?''
You and 2 or more friends: ''BANZAI BANZAI BANZAI''
Shout this repeatedly until phone call ends. Whispering also works well.
You can also use the word in normal sentences