What's the context? What books?
Nothing fancy. I wrote "Keeping Murphy Out of Your Aquarium" in 1996, it's about 74 pages, simple, covers biological filtration, pH, fish temperament choices, a good beginner's book according to the pet store that was using it to train her employees. There are a lot of very advanced aquarists on this site, but that is not a common phenomenon anymore. I was going to sell my hex tank, which has an established biological filter. The lady buying it did not have a clue what a biological filter was. I decided to keep the tank, told her I'd send a copy of Murphy via pdf just for the inspiration.
I let Murphy go out of print in about 1999 when enteric septicemia was running thru my tanks, it seems that southeast asia cleared it up on their end since but for many years I have not bought fish if I could avoid it. I couldn't figure out whether to update Murphy's disease section (including changing recommended meds as many are no longer available and/or ich is immune to them), or what to do, so I let it go out of print, and I had a busy aquarium and pond service to run. Fish books do not stay in print with major publishers. I did a rewrite for a british publisher in 2001 and a few years ago I scooped up enough copies off amazon for all of my grandchildren. It's not a great book, I lost copyright on anything in it, but I wanted the kids to see it.
The other book I would like to put out is a children's book, illustrated with water colors, about a pet store visit. It's called "All About My Day". Maybe 25 pages. When I painted those water colors color copy machines had just gotten into office supply stores. So I have copies of the paintings in a home bound copy here, the originals are in my safe deposit box.
I just want to do things I enjoy to make money. I have zero desire to be fully retired. Boring. I like to fiddle at a lot of things, i do web design, some graphics, used to do animated graphics but quit buying software and I have no time for it. I fix sewing machines, I grow plants for the native plant sale, I propagate succulents. And about anything else that will propagate easily.
And I have zero interest in a reverse mortgage. I am probably not as old as your parents, and I still make my living climbing and fixing waterfalls young man. My grammar has really deteriorated, lol.