It's WP 8.0 you're using, right? What you're seeing there is placeholder text. It's just indicating that there's an appointment set for the particular day, but the text is random "lore ipsum" phrases (the language is Latin btw). To see the "real" text, you need to tap the day to open the appointment.
This behavior will change with WP 8.1 though. All the placeholder texts have been removed, colored lines now indicate that you have an appointment on a certain day (in monthly view). The colors used for these lines match those you have defined for your different calendars in the settings.