[m.]; the First “Day of Creation,” described in Bereshit 1:1-5
In the beginning, “E-lohim,” G-d created the “Heaven” and the “Earth.” And the “Earth” was formless and void, and the Divine Presence hovered over the “waters.”
G-d said “Let there be ‘light’ ” – and there was “light.” And “E-lohim,” G-d saw the “light,” that it was good and separated between the “light” and the “dark.” And G-d called the “light,” “Day” and the “darkness,” “Night.”
An “Evening” and a “Morning” passed, completing One Day.
Note that a different term is used for “Sunday,” the first day of the week, using the ordinal number, “first” rather than the cardinal number “One;” namely, “Yom Rishon.” Whereas, the first “Day of Creation” is called the “Day of the One,” to emphasize that G-d alone created the Universe and all that is in it.