Difference between Subdominant and Perfect Fourth

[patthedog]

In Module 8 of the beginners course, the intro mentions "Subdominant", but the rest of the exercises go on to refer to "Perfect fourths". What is the difference between these two terms? In which context would one choose one term over the other?

[Quentin]

Perfect 4th is the name of the interval, whereas subdominant is its function within the key. It refers to the same distance from the tonic, it's just two different names for 2 different uses.