What does it mean when a person says they're spiritual but not religious?

It usually means that they don't know what they're talking about. The secularist by not wanting to be associated with a specific religious organization thinks he or she is non-religious. They're still religious if they believe in a worthwhile afterlife provided by some unspecified agency. There are religions of many people and religions of one person.

Exceptions will exist in those that have not yet considered or have rejected the possibility of afterlife. They can be spiritualists without being religious. Another exception is those that have a pessimistic view of afterlife. It has to reflect optimism. All of these exceptions are examples of proto-dabbler belief: which is the proven precursor to the Buddhism of today.

“Spirituality” is a human faculty. An ability, a category of experience, a realm of endeavor. Generally the scope of spirituality is metaphysical truths beyond the scope of materialism.

The “spiritual” person is thus, concerned with, and interested in, questions such as whether or not there is a God, what their relationship with God is, what salvation entails. Or questions about the deeper purpose of life. Nontheistic people might be interested in the ground of being, what enlightenment is, how it is achieved. Some are interested in spirits, gods, other unseen entities. What happens after death is a pretty universal question. Deeper levels of ethics and connection are pretty universal.

“Religion” is a social construct. It aims to normalize and regulate the scope “spirituality”. It renders certain forms of spiritual inquiry not only aberrant, but evil. It also renders certain human experiences not only aberrant, but evil. It extrudes parts of our spiritual experience and uses them to normalize social behaviors. It also uses parts of our spiritual experience to support, defend, and rationalize political choices.

So the “religious” person is a type of “spiritual” person, but concerned more about being a model adherent to a social organization called a church, temple, synagogue, zendo, hoff, whatever, than spiritual truths and wherever those truths might take one. Religious people often dislike and alienate spiritual people because they transgress social and political norms. Spiritual people often avoid religious people because they don’t want to get lost in the weeds of compliance to arbitrarily decided social and political norms.

For me for example, it simply seems logical that their is more between heaven and earth sort of. No religion needed. Like it's impossible to rule out the existence of "God" for example. What I do know, is all forms of earthly believes in a religious sense is no narrow minded and tiny it doesn't actually even leave room for the possibility of an actual God. It's kinda funny when you think about it, Religion on earth is anti God.

For the most part, it means the person is making up what they want to believe.

No understanding, no knowledge, no open mind to understand what's true instead of what feels good or is the fad of the moment.

There is some truth in what @CopperCicada posted below (other than his take on "religious" persons, which is just bias on his part)... but only in bits and pieces.

Religion follows one God that their beliefs and teachings are based around. It is organised, it has priests/religious heads or something to carry the work of spreading its teachings.
Spirituality is all encompassing belief in something bigger than ourselves.

I take it to mean they believe in some kind of spirits or believe in some kind of universe energy.. But they do not believe in an actual God ( person )..

Often you have to ask them to enplane it in more detail to get a clear indication of what they actually believe..

they don't follow the dogma of any known religious institution but their own findings from searching?
or they jsut think it sounds cool and have no idea what they re talking about either.

Believes in that, in the imaterail and abstract, in thoses senses, but not follows any organized or specific believe system

[media=https://youtu.be/rY7wEu93QYw]

What just happened to SW earlier? It was under maintenance?

A great connection with the Universe
[media=https://youtu.be/UABKw6xU2r0]

They like butt secks and axe body spray

It's ultimately meaningless, whatever the specific individual means by their own personal take on that cliché

Superstition is ultimately superstition, whether you practice it on your own, or in a social club, and whether or not you use it to try to meddle in the affairs of others

Moreover, the imaginary remains imaginary, regardless of where it is arbitrarily placed on a liberal-conservative spectrum

Superstition just hinders the evolution of humanity and civilization

The same thing an architect means when he thinks he can dump a bunch bricks, cement, wood, gyprock, pipes, wires, roofing tile, etc. into a pile and expect a house to come out of it. What he really means is he doesn't know what he's doing

Religion is just believing in someone elses thinking on how they think it all works, I just use my senses and use the signs and signals to what is going on around me, I think our energies are all connected is some way.