'flat-rate' originates from the combination of 'flat,' meaning 'level or even,' and 'rate,' meaning 'a fixed charge or payment.'

'flat-rate' evolved from the concept of 'flat' meaning 'even' and 'rate' as a fixed charge, becoming a common term in modern pricing strategies.

Initially, it meant 'a level or even charge,' and over time it evolved into its current meaning of 'a single fixed fee for a service.'