Text is a sequence of characters read to form words, phrases, lines or sentences of which have not been arranged this way by chance, but have been produced by a person and with intentions to create something that contains meaning which is open to interpretation
Sans and Sans-Serif Fonts
Serifs are semi-structual details or small decorative florishes on the ends of some of the strkes that make up letters and symbols. Sans means to be without. So in essence the difference between Serif and and Sans-Serif fonts are the decorative florishes in text design present on the Serif text font
Definition of Interactivity
Interactivity is the communication process that takes place between humans and computer software. Programs that run without immediate user involvment are not interactive, they're usually called batch or background programs. Games are thought to be the ultimate for of interactivity as they require a large amount of player involvemnet for the program to function as intended.
Interactivity has been shown throughout this book as the user (in your case reader) must give directions for the book to continue forward onto the next page.