Evening – Erev
Morning – Bo-ker
When the Bible writes, “and there was an evening, and there was a morning, one day. It means the absence, in a form of the evening, always comes before the being. The evening is an example of a minus, a pre situation, and the following morning reflects the plus. Only a unification of an evening and the morning after it, are considered to be one day.
An evening alone is not considered to be a day, nor a morning alone is considered to be one day, Only both opposites together can be considered as one day.
Also, please note that the days which are mentioned in the Bible, Genesis chapter 1, are not equal to “our days”, which have 24 hours, but one biblical day is one unit of completion.