It's not just "used in many ways," it has several definitions. The one that almost everybody uses -- including the Fed[0], US Dept of Labor[1], and the ECB[2] -- is about rise in prices. Nobody is saying that your definition is bad or wrong, but to claim that it's the only (or even primary) one is disingenuous.

[0] https://www.clevelandfed.org/center-for-inflation-research/i...

[1] https://www.dol.gov/general/topic/statistics/inflation

[2] https://www.ecb.europa.eu/ecb-and-you/explainers/tell-me-mor...