God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.
Genesis 1:5 (NKJV)
God (‘ĕlōhîm) called the light Day, and the darkness Night.
The word “day” is translated from the Hebrew word yôm, which has been interpreted as day, time, or year throughout the rest of the Scriptures.
The word “night” is translated from the Hebrew word layil. This word is usually translated as night, but has also been interpreted as midnight or season.
It is important to note that evening was listed before morning in sequence here. This is why Jewish days officially begin and end at sundown.
Daily Bread for Women 