Currently, am working on making a dynamic site compliance. I use WAVE Tool chrome extension and manual testing for keyboard navigation. I am hearing a lot about Accessibility Score number (which I have no idea about). Upon googling, I did see that there are some sites who does this and gives us the report. But wanted to check with the community here and see what this score is about and how to get it (for free) if possible? any tips/suggestions, greatly appreciate it!
An "Accessibility Score" is a marketing thing. Most companies that sell an accessibility tool also generate a "score" that is unique to their testing rules. If they have 100 rules that test for accessibility and you pass 75 of them, you'll have a score of 75%. If you were to run your same app through someone else's tool, you might get a score of 65% or 85%. There's no standard.
And the score is usually not just a simple number of rules passed compared to rules failed. Some failures have more "weight" because they're more critical than other rules. So you might actually pass 75% of the rules but get an 80% score (because the rules you passed carried a higher weight) or you might get a 70% score.
Most free tools, such as WAVE (as you mentioned) or aXe, don't generate such a score. They just give you the results of what they found wrong.
And keep in mind that most accessibility tools can only catch about 20-30% of accessibility issues. The rest have to be found manually.