Any one of those, and more.

The most common, I think, is "you'll do for now but I want the option to back out if someone I think is better shows up," which is why if I'm serious about someone it's a deal-breaker.

Sounds like a "friends with benefits" scenario to me.

It means they don't want a commitment. Period

On rare occassions it might mean they might be insane, but they don't really want to go to a mental hospital involuentarily.

If I was looking for a commitment with someone, and got that statement, would just walk away. My take is they are still looking, and I am not the one.

Kinda working through all this in my mind and life right now. What I do know is that there is no way I should be in any kind of long-term committed relationship right now. I'm just too fucked up. What I'm not sure about is whether I can handle a physical relationship. Don't know if I could maintain that boundary. Until I figure it out gonna try and keep my distance from both but I can see how you could be intimate with someone, both physically and emotionally, without wanting anything long term. Communication and honesty still hugely important. It's not necessarily selfish.

Means they fancy you - a little, but are still looking waiting for someone better because they won't be with you through think and thin.

Some clarity on this issue can be had by thinking of a bacon and egg breakfast. The chicken made a contribution, the pig made a commitment.

This is how it has become for me. I can't commit to a relationship any more, there just isn't enough of me left. But I'm willing to contribute as long as it is working for both of us.

It means run.

My interpretation is that commitment in this context is typically synonmous with "monogamous relationship."

It means they want sex. Period.

As someone who has used this line before, it has always been a way of saying “I’m not sure how I feel right now”. Of course this is coming from a woman’s perspective so I’m not sure if there are typical gender differences when it comes to addressing this matter. “I don’t want commitment” has never implied that I was looking for sex but that I wanted company until I had more time to figure things out (because I was unsure of the situation). I have ended up dating individuals and committing after deciding that it was what I wanted, but I have also broken things off. I think that hearing this from someone is difficult and unpromising. It’s perhaps a sign that someone is in transition and needs time before they can commit to anyone, but it can also be a sign that they’re afraid to commit before finding the right person.

My go-to reason for this is "I don't want to spread myself any thinner" but it's more than that, the idea with living with someone or being obliged to see the same person everyday no matter what leaves me cold as does monogamy. I gave all a good shot, the relationship with my daughter's mum lasted 11 years before that I was with someone for three.
The common belief is probably that I'm a "player" or just need to meet the "right ONE" so I see how it's hard for someone that takes an interest in someone like me not to take it personally.

It means they're Just Not That Into You

It surely means they don't want to be in a relationship and if that is not what the other party has in mind...then they should not waste time, with this person! I wonder what happened to being friends with somebody. Friendships are so important toward our development as a human being. Maybe, we don't fully understand that until we are old?

What it means is I want to screw you NSA and we can be friends, but when this cools off I want to move along and we will both go our separate ways. In other words, I wanna milk the cow without actually buying the cow. Gimme free milk and it's all OK as long as we think the same. Women either want the same thing at this point, or they go with it coz they all think deep inside "I can change him." Changing him usually does not work.

Depends on the person saying it. Could mean you're not the one they want to commit to, or that they don't want emotional entanglement at that time in their lives - maybe indefinitely, or that they really don't want a commitment - to anyone -ever !

In general it means they don't want the responsibilities that come with a commitment. There can be many reasons, some less honorable than others. Still, they were honest enough to say so.

When I say it, it means I'm afraid of getting into a long term relationship because I have been hurt so badly. It means I don't want to count on you or anyone else because I already know the likelihood of being let down, it's 100%. It means I am currently not willing to sacrifice myself to this relationship.

And I think (but I don't know) that if you're not willing to see me through my doubts and fears, you won't be there when I change my mind, either. But that's the gamble, isn't it?

I just wanted you to know it isn't always about sex.

They don't want any responsibility for holding up their end of a relationship.
That, and they want the freedom to fuck around.

They're not that into you - at that point in time. That may change. But at that point in time: they're not ready to dedicate whatever free time they have with you.

@Akfishlady it means they're not available in any meaningful way for whatever reason.

It means a relationship with you means next to nothing and they are looking for someone else. Run as fast as you can unless you are happy being a booty call/therapist

It means they'll be looking over your shoulder at a party to see if there's anything better around.