Definitions do change, but this one hasn’t. 99% of people I see using the term “open source” in the present day are using it to mean software that you can freely modify and redistribute. For proprietary software with publicly readable source code, the term “source available” is used instead.
Where are you getting that 99% from?
Personal experience? I have never seen any notable case of a software project describing itself as “open source” that wasn’t also free software.
Companies that want to publish their source code but not give you the right to use it however you want, e.g. Cockroach or (my former employer) Materialize, are described as “source-available” instead.
My personal experience is 100%-0%. I've yet to see a project that uses "open source" as a synonym for FOSS or OSI. There are a lot of projects out there that use "open source" meaning "open source". HN comment section is always in outrage.