A Missal was a ceremonial mass book used by priests during typically a Roman catholic mass containing a set of prayers, songs and rules that were to be used for everyday mass as well as for special occasion masses and on important days of the catholic year.

Sources:

Funk & Wagnalls New World Encyclopedia. “Missal.”https://ezproxy.latech.edu:2068/eds/detail/detail?vid=1&sid=b3042f1b-3747-4614-8494-8349340154e6%40sdc-v-sessmgr02&bdata=JnNpdGU9ZWRzLWxpdmUmc2NvcGU9c2l0ZQ%3d%3d#AN=mi118900&db=funk

Editors of Encyclopedia Britannica. “Missal.” Encyclopedia Britannica,https://www.britannica.com/topic/missal”>https://www.britannica.com/topic/missal