Goodreads defines each star as this: 

1 star: did not like it
2 stars: it was ok
3 stars: liked it
4 stars: really liked it
5 stars: it was amazing

Note: My average Goodreads rating (as of July 2018) is 3.38. 

I stick pretty close to this scale but I'm a little more passionate. 

1 star: Not only did I not like this book but I might not have even been able to finish it. Or, if I did finish it, it was only because I like to punish myself for picking such bad books. So more than likely, if I finished this book, it was a hate read. 

2 stars: It was ok. It wasn't a complete "hate read" but I had parts that I struggled to get through. The bad outweigh the positives BUT I found enough to enjoy so that I kept reading. 

3 stars: I liked it. I found it enjoyable and it kept me interested. The problems I had with it were minimal--or at least issues that I could live with. {The majority of the books I read fall in this category.}

4 stars: I REALLY liked this book. It had me hooked from the start and I wanted more. Character development is a huge deal to me so to get to this level there needs to be some great characters that I love--and love to hate. {2nd most common rating I give.}

5 stars: OMG I want this book to come to life. I RARELY buy books anymore (I'm a hardcore library e-book reader) but I can see myself buying this book and maybe even everything else this author ever writes. I can't stop thinking about this book and I don't think I can do anything else for at least a week as I slowly process everything I just read and try to transition back to real life.