What is constituted as a "Week?"

Everytime we have class, it constitutes that start of a new "Week." We have this class on Fridays so it can get confusing.  For example, although a given Tuesday may be the second week of a term, it is still considered "Week 1" of this project until class later that week on Friday, which sets "Week 2" of the project in motion.  And the next Friday starts Week 3 of the project, and so on.