What do the unit codes mean?

Each unit has a unique code that consists of 3 parts. Take for example BS1D01 Biblical Theology

BS - This unit is part of the Biblical Studies field. The other two fields are CT - Christian Though and CM - Christian Ministry.
1 - This unit is in the first semester. 
D01 - The unit's unique identifier.

The unit CM2D01 - Engaging With Islam would be:
CM - Part of the Christian Ministry field
2 - The unit runs in the second semester
D01 - Engaging with Islam and not Making Disciples (CM2D02)
A unit code may sometimes omit the semester identifier when simply referencing the particular unit (CMD01).