Some people say, "I'm spiritual but not religious". It puzzled me for a long time what they could mean.
Religion isn't belief in a god, because not all religions have gods. It's not belief in supernatural beings and realms, because that would make channelling a religion. It's not submission to authority in matters of belief and action, because that would make kindergarten a religion.
Religion is belief in teleology - a purpose to the universe. A goal, plan, guiding principle with a target. Though to believe in a masterplan is not necessarily to believe in a masterplanner.
To that extent, anyone fighting a battle where they belive victory is inevitable has a religion.
Teleology is a form of amimism, as is the anthropomorphic belief that morals exist "objectively" outside of societies, but not all animisms are teleological.
Often, there's an attitude towards the supposed masterplan - that to push the plan towards completion is "good" and to oppose it is "bad". Or conceivably the other way around, eg. satanism.
Hence the relation between religion and "faith" as in "to have faith in X". Faith in this sense is an attitude of trust - faith in the goodness of people, in the reliability of an information source, and in History moving itself forward towards a better world.
This implicitly presupposes that the masterplan is knowable to humans and (at least in part) known to the beliver. Thus someone with religion believes they have special insight which common folk lack.
It also presupposes that humans in general and the believer in particular have the power to help or hinder the plan. Thus the religious believer believes they personally have godlike power to affect all reality - through ritual, prayer, meditation etc. This is the connection with belief in the supernatural - to believe in a masterplan carried out by willpower presupposes a belief in magic.
Which in turn means the people they identify as the enemy (a foreign nation, a rival church, an unpopular minority, an imaginary conspiracy etc.) also have the same power, though they may lack the special knowledge. To the christian, hindus work against god.
Religion here involves the elevation of the concerns of a sect (or an individual) to cosmic levels of importance. The flipside of this is the reduction of the universe to a human drama - storms as angry gods, earthquakes as punishments, astrology, fate etc.
Religion is attractive partly because it offers simple answers to difficult questions, but also because it makes the believer feel special - even in a nation of believers - as one who both knows the masterplan and is part of it. Thus even without atheists, the believer needs notional unbelievers (or less fervent believers) to be superior to.
When a person says they have spirituality but not religion, the minimum they mean is they are aware of a teleology.
Defining the teleology, being able to promote or retard it, defining good and bad by this ability, having enemies defined by it, being part of community of believers, superiority to nonbelivers - all these are nonessential options, and can be added and subtracted as needed.
Spirituality in this sense then is minimalist religion.