Definition & Meaning of "holy moly"in English

What is the origin of the idiom "holy moly" and when to use it?

Holy moly is an exclamation used to express surprise, shock, or amazement. It appeared in American English in the early 20th century, likely as a playful euphemism for "holy Mary" or "holy Moses," replacing sacred names with a harmless, rhyming word. The phrase became popular in newspapers, comic strips, radio, and everyday speech, especially from the 1920s onward, and was often used in lighthearted or humorous contexts. Today it sounds whimsical, slightly old-fashioned, and inoffensive.