In the bible, what does "this generation" mean? (reference below)?

It obviously is that Generation during the time of Jesus. Yes Peter and a couple of others saw Christ in his glory as Jesus said. Also only a handful witnessed the ascension of Jesus to Heaven to sit at the right hand of the Father. In AD70 many of that Generation was alive to see the total destruction of the Temple by the Romans and many lived through the destruction of Jerusalem by the Romans which with the destruction of the Temple ended the World as they had known it.