This is Ember week in the traditional calendar, traditionally days of fasting and abstinence at times marking the change of the seasons.
You can read more about them here..
In the Ordinary Form, St Januarius is remembered. Here is the entry from the traditional martyrology:
"At Puzzoli, in Campania, the holy martyrs Januarius, bishop of Benevento, Festus, his deacon, and Desiderius, lector, together with Sosius, deacon of the church of Misenum, Proculus, deacon of Puzzoli, Eutychius and Acutius, who were bound and imprisoned and then beheaded during the reign of Diocletian. The body of St. Januarius was brought to Naples, and buried in the church with due honors, where even now the blood of the blessed martyr is kept in a vial, and when placed close to his head, is seen to become liquid and, bubble up as if it were just taken from his veins."