What it used to be called:

Diapers

What changed:

Disposables soaked up most of the market.

Centuries ago, the word diaper had nothing to do with bottoms. It referred to a fabric with a distinctive geometric pattern. This kind of fabric was used in the garment for babies; that garment came to be known as a diaper.

These days diaper generally means the disposable kind – an invention that first appeared after World War II.

When the language required a new word for the old thing, cloth diaper was born.

An early use:

"Playtex tests confirmed by the Good Housekeeping Institute show that Dryper disposable diapers are more absorbent than ordinary cloth diapers." — Advertisement, Los Angeles Times, July 12 1960