This is the opportunity 'of a lifetime'. = This sort of opportunity comes along 'once in a lifetime'. [=this is a very rare opportunity]
a baseball player's 'lifetime' batting average [=batting average measured over a baseball player's full career]
She was presented with a 'lifetime' achievement award. [=an award for all the work she has done in her life]
(..) how much you love her. You don't know his story. I don't care. You should. Tom loved a woman more than most men can in two lifetimes. They had a good life started together. She was pregnant with a little boy, birth got the best of them. Tom's been alone ever since. Lone wolf. (..)2012 Mud