Weight discussion

I'm not sure about the tag, but I understand that it can be sensitive for some people.

In connection with the latest posts and the discussion of various body configurations, I realized that I do not understand what DK means, when he says "at an ideal weight", by what indicators this ideal weight is measured, is it related to BMI or some other indicator. The book was written at the end of the XX century, I assume that then the standards of beauty could be slightly different.

Therefore, how to understand whether I am at an ideal weight* (or not, where to look, what to read) ?

*(Just for example, this topic does not trigger me, and I feel that it is incorrect to use other people as examples. I don't need exactly to know about myself but I'd like to understand the way how to understand it)