'Generation' in the Bible

He sighed deeply in his spirit and remarked, "Why do those living today demand a sign? I tell all of you with certainty, no sign will be given to this generation."

If anyone is ashamed of me and my words in this adulterous and sinful generation, the Son of Man will be ashamed of him when he comes with the holy angels in his Father's glory."

Jesus told them, "You unbelieving generation! How long must I be with you? How long must I put up with you? Bring him to me!"

I tell all of you with certainty, this generation will not disappear until all these things take place.