Introduce "subject" before defining "subject"

[camerons]

Referring to the following sentence:

By contrast, here's that same sentence written in passive voice, where the subject of the sentence is the target:

This example has introduced the term "subject" before defining what the subject of a sentence is. (I was one of those kids looking out the window during English classes in primary school, and I get lost by this sentence. I need to head to google to work it out.)