The literal meaning of  一期一会   is "once in a lifetime oppotunity."
This phrase is used to indicate that an event or occasion
should not be missed because it is unlikely to happen again.
At Japanese tea ceremony, the host should serve tea to
guests just like once in a life time encounter.
Because of one meeting would never happen again.
This term was started by first tea master"Senno Rikyu" to
keep people to remember the most important attitude
to participate to tea ceremony, but also a lot of Japanese
educators consider this term as their motto.