“Hi, Bob, long time no see!”
“Yeah, I guess the last time was at the Jill’s wedding!”
“Long time no see” is a cute greeting to use when you haven’t seen someone in a long time. It’s not really grammatically correct: “It’s been a long time and I have not seen you.”
「あら、ボブ、久しぶりね。」
「そうだね、ジルの結婚式以来かな？」
Long time no see は久しぶりに会う人に使うカジュアルな挨拶です。厳密に言うと文法的には正しくはありません。 It’s been a long time and I have not seen you. 「長い間、見ていない。」
