Green’s Dictionary of Slang

soap opera n.

also soap, soaper
[the original 1920s radio show, The Goldbergs, was sponsored by US soap manufacturer Proctor & Gamble]
[1930s+] (orig. US)

1. a radio or TV drama series, e.g. The Archers, Coronation Street, which tells the interminable tale of supposedly ‘ordinary life’; thus soap v., to watch a soap opera.

2. attrib. use of sense 1.

3. also in fig. use, of anything endlessly repetitive, albeit melodramatic.

In compounds

soap-freak (n.) [-freak sfx]

[2000s] (US) a fan or devotee of a radio or TV drama series.