What does the word solid mean (the synonym)

two factors or characteristics of a chapter that might make it difficult to read would be words i don't understand, or if i don't fully understand what's going on in the chapter. strategies i can use to get through the difficult material would be a dictionary, and re-reading previous chapters to get a better grasp of what the author is trying to say.

- "the basic difference between keywords and subjects is that subjects (or "subject headings") have been predetermined, while keywords have not. a keyword is an easy place to start because you can use any word that seems to fit your search; this is called "natural language" searching."