“Yom Shishi” – the sixth day of the week; very similar to, but slightly different from the Sixth Day of Creation, Yom HaShishi; the similarity is due to the fact that according to Jewish Tradition, the Sixth Day of Creation was indeed Friday; the difference, the letter “heh,” the fifth letter of the Hebrew Alphabet, the definite article meaning “the,” is due to the fact that the Sixth and Final Day of Creation was singled out, as RASHI explains, to indicate that heaven and earth were created only on condition that the Jewish People accept the Five Books of Moses (Midrash Tanchuma 1).
An alternative, but similar, explanation is that the term “HaShishi,” meaning The Sixth, that special Sixth, refers to the Sixth of Sivan, the Holiday of Shavuot, on which the Jewish People accepted the Torah, and on that day it was as if the Creation was solidified; that is, reality somehow became more permanent because, again, the lessons of the Torah are the purpose of Creation (Shir HaShirim Rabbah 1:9).