What is the 420 in dating?

Excuse me, could you elaborate on what the significance of "420" is in the context of dating? I've heard it being used in conversations and on social media, but I'm not quite sure what it stands for or represents. Is it a code for something specific? A reference to a particular date or event? Or perhaps it's just a slang term that has gained popularity among certain groups? I'd really appreciate if you could shed some light on this for me.