What does J mean in NMR?

Excuse me, I'm curious about something I came across in my research. I'm wondering, when we see the letter "J" used in the context of NMR, or Nuclear Magnetic Resonance, what exactly does it represent? I understand that NMR is a technique used to study the structure and dynamics of molecules, but I'm not clear on the specific meaning of the "J" notation. Could you please explain it to me in a concise manner? Thank you in advance for your help.