表达 “a jam session” 指 “音乐家们进行非正式的演奏”，这类演奏通常是 “没有经过排练的即兴演奏”。这个表达中的动词 “jam” 的意思是 “与他人即兴演奏”。

例句
I’ve just got a new guitar. Do you want to come round for a jam session tomorrow?
我刚买了一把新吉他。你想明天过来和我一起随意弹弹吗？

I was in the bar, and these musicians just started a jam session – it sounded amazing!
当时我在酒吧里，这些音乐家们刚刚开始即兴演奏，听起来特别棒！

We had a jam session yesterday, and I think I’ve got an idea for a new song now.
我们昨天进行了一场即兴演奏，我觉得我现在找到了新歌的灵感。