Short answers, pulled from the story.
The Latin word religio first appeared in Roman texts to describe a sense of obligation or duty, not a system of worship. Cicero used the term to mean careful consideration of divine things while Pliny the Elder applied it to elephants showing respect for the night sky.
Clifford Geertz defined religion simply as a cultural system in 1973. Émile Durkheim described it as beliefs relative to sacred things in his 1912 book The Elementary Forms of the Religious Life and E.B. Tylor proposed in 1871 that religion meant belief in spiritual beings.
Four religions account for over 77% of the world's population according to demographic data from 2015. Christianity remains the largest with approximately 2.3 billion followers followed by Islam at 1.8 billion Hinduism represents 1.1 billion adherents while Buddhism accounts for 0.5 billion globally.
Japan had no indigenous word for religion when American warships forced treaties demanding freedom of belief in 1853. No one self-identified as Hindu or Buddhist before the 1800s proving these labels are modern inventions imposed on ancient traditions.
The Islamic Republic of Iran defines itself explicitly in religious terms while other nations remain secular. Most Muslim-majority countries adopt aspects of sharia affecting up to 23% of the global population and China and Japan maintain largely secular governments where religion exerts minimal political influence.