Soap operas are called soap operas because early radio dramas were often sponsored by soap and other household-product companies, and the stories were melodramatic enough that the “opera” label became a playful shorthand.

Why the name stuck

The “soap” part points to the advertisers that funded these programs, especially in the U.S.. The “opera” part refers to the exaggerated, emotional, cliffhanger-heavy style of the stories, not to actual opera music.

In plain terms

They started as serialized daytime dramas, and people began calling them “soap operas” as a nickname that stuck over time. Today, people also shorten it to just soaps.

TL;DR

They’re called soap operas because they were originally sponsored by soap companies, and their plots were as dramatic as an opera.