The philosophy of life called secularism (a term introduced by G. J. Holyoake in the 19th century) means the placing of emphasis on living our lives in the here and now in accordance with the evidence of our senses and our reason and not allowing ourselves to be carried away by wish-fulfilment into believing things just because they sound nice or are what we might like to be true.
Secularists are also called freethinkers, since we like to think for ourselves, and sceptics because we question traditions and all people who set themselves up as authorities or experts, and rationalists because we rely on reason applied to the evidence of our senses. For most matters of everyday life this amounts to little more than common sense.
For aspects of the world beyond everyday experience, such as on the large scale of galaxies, the small scale of atoms, the distant past of evolution, the possible future consequences of our actions, and the often mysterious workings of our minds, we have to rely on the findings of science, though not uncritically. There is still a lot we do not know, and we must keep an open mind. Some secularists are qualified scientists, and most like to keep up with the latest findings of science.
Secularists are also humanists: this term emphasises the need for all of humankind to live together in reasonable harmony, and the ideals of kindness and tolerance that make this feasible. Humanist ideals include, for example, bettering the lives of people, through medical knowledge and social reform, promotion of good government in place of corruption, supporting equable rights for women and the poor, preventing the exploitation and indoctrination of children. People who promote these moral ideas, based on reason rather than religion, are sometimes called ethicists.
One of the main origins of religion is in out-of-date ideas of the way the world works, based on wish-fulfilment.
We experience the death of loved ones it would be nice to think that they might live on in some way other than in our memories (this leads to ideas of life after death like spirits, ghosts, angels and reincarnation).
We fall foul of chance accidents and find life a struggle to survive or to achieve anything worthwhile it would be nice to think we were all part of some grand plan by some benevolent father-figure wise beyond our comprehension (this leads to ideas of a god, fate and submission).
We may become victims of injustice it would be nice to think that such injustices were all put right in some way (this leads to ideas like karma, or a day of judgment).
Such ideas have been written in "holy" books (Torah, Bible, Koran) that are treated as if every word is literally true. This fundamentalism leads to rivalries and hatred between people. Such ideas are often forcibly impressed on children from a very young age in a manner that secularists regard as indoctrination or even child abuse.
Belief in a god or gods is known as theism, so secularists are often called atheists (or unbelievers, or infidels), even though this may only be a small part of their world-view. Some secularists may be deists, believing in a creative force or first cause, or agnostics (a term invented by T. H. Huxley), meaning they don't know. A new term that is becoming popular is bright, meaning someone with a naturalistic outlook.
The term scientism is sometimes used by religionists as a disparaging term, implying that secularists are dogmatic in their scientific beliefs, but this would be plainly contradictory to the principles of scientific method which require us to be open to change our views in the light of new evidence. Other terms used in a similar way are reductionism and materialism, meaning to imply a lack of humanity or 'spirituality' in those who rely on science, but this is far from the reality.
Some extreme religious believers tend to identify atheists and secularists with pagans, and even satanists, but this is just absurd prejudice since such people are theists, satan being a type of dark god and pagans tending to believe in personifications of natural forces. Although much is still written about atheism and theism, for most secularists it is a dead subject, settled long ago. Since there is no evidence for the existence of supernatural beings theology is seen to be a completely vacuous subject.
Worldviews that have no place for gods or superstition can be traced back to antiquity. It seems probable that in any community there have aways been down-to-earth practical people who see the tales told by priests and mythmakers as just that fiction.