According to wiki, the term has different meanings. One it this:
Natural religion most frequently means the "religion of nature", in which God, the soul, spirits, and all objects of the supernatural are considered as part of nature and not separate from it.
Even though it says that is the "most frequent" meaning, I suspect that when you hear the phrase the intended meaning is something else. Here's another definition from wiki
It is also used in philosophy, specifically Roman Catholic philosophy, to describe some aspects of religion that are knowable apart from divine revelation through logic and reason alone (see natural theology and Deism) for example, the existence of the unmoved Mover, the first cause of the universe.
Wiki goes on to give other definitions. These days I think the phrase is often used to convey something like this (again, from wiki). Think of fervent activists like Greenpeace.
A reverent form of nature worship, embodied in a statement by Frank Lloyd Wright: "I put a capital N on Nature, and call it my Church."
Using my own words, I think it is most often intended to mean a set of morals or values derived purely from "natural" (as opposed to supernatural) foundations. Unlike Deism, it posits no God, because there is no God, only nature. Also called things like "humanistic naturalsim:"
Humanistic naturalism is the branch of philosophical naturalism wherein human beings are best able to control and understand the world through use of the scientific method, combined with the social and ethical values of humanism. Concepts of spirituality, intuition, and metaphysics are considered subjectively valuable only, primarily because they are unfalsifiable, and therefore can never progress beyond the realm of personal opinion.
Edited by Moronium, 10 June 2018 - 08:09 AM.