Question: Why is a the book used for learning Torah readings called a Tikkun?
Answer: Good question. I do not think I’ve ever seen an answer quoted from a specific source but I would think it is because you can fix mistakes with it. Tikun - means a correction or fix. Other forms of the name for this book are Tikun Sofrim and Tikun Korim. I suspect that it used to be called just Tikun Sofrim which was what the Sofrim (Torah scribes) used to fix mistakes in a Torah. Some were used to copy from when writing the Torah Scroll. In addition to having the lines set up for the Torah they had an indication on the side showing how tight or spacious the line was for the sofer to determine if he needs to compact his writing or not.
All the best,
Rabbi Y. Benyowitz