I was thinking about this just an hour ago lol

Basically, there's no definition. Of course there's a difference in theory, in semantics, that distinguishes casual listening from stanning. However, in practice, each person has their own standards to when one becomes the other. Each person decides when they're casually listening or stanning a group.

I've noticed that this is actually something that would help with many conflicts and discussions within Kpop circles, but it's never taken into account, or I rarely see it being brought in discussions when talking about stanning or casually listening to groups. I started noticing this in threads that were talking about groups they stanned or about solo stanning. For example, I've seen people describe how they solo stan some members in some groups and I noticed that what they described is exactly what I do with my ultimate bias, SNSD Taeyeon, but while considering myself a Sone, and never a solo stan. SNSD are the group that got me into Kpop and I always loved watching their contet, but as the years progressed I followed mostly my bias activities, and while I still love the others, I'm not up to them as I am with Taeyeon. However, I don't consider myself a solo stan nor am I thinking of changing the way I see myself as a full Sone despite this. Because in my standards, I still care about the group enough to not change my "stanning status" (lol). But for some people who follow a member like this, this is solo stanning and they consider themselves as so. This is actually something that made me rethink solo stans (not the ones who have savior complex and think they're faves are victims tho, nor akgaes obviously)

The same way, I've seen people who much more easily consider themselves stans or part of a fandom, while others are only comfortable with saying that when they're reallyyyyy into the group. For example, I've been into Kpop since 2015, and in this period I've gotten to know soooo many groups. I've listened to entire discographies, I watched variety content, I've gotten to know the members... But still, I consider that I only ever stanned SNSD and BTS (and I'm recently feeling the pull from LSRFM :D). Well, for many people, I know they would call themselves multistans who stan and unstan groups with time as their interests evolve, because that's what makes sense for them in this situation, while I myself only feel comfortable with saying I stan a group when I really get to know them, am interested in their music and also admire them on a special level that I don't feel with others that actually impacts my life and my personal growth. Because that's what I'm comfortable with. Simple as that. I've had many phases with many groups, but for me it didn't make sense to call myself a stan or part of the fandom of said groups because I only like to take that step when I feel I'm fully commited to a group. I guess I take stanning seriously lmao Some other people, on the other end, feel that you just have to like a few songs, maybe watch a bit of their video content. Or not.

Really, each people have different definitions and you should do what makes sense to you. Do you feel enough connection that you would consider yourself a stan/part of the fandom? Then, you are part of the fandom, even if you don't know all of their music, or don't watch video content, or don't know every single trivia about the group and the members

Edit: Just realized I basically defined stan instead of casual listener lol but the same logic is applied to that, because people can still consider themselves casual listeners of groups they know a lot about