What is a italicized clause?

There's no such thing as an "italicized clause" in the grammatical sense. It's important to understand the terms:

* Clause: A group of words containing a subject and a verb, forming part of a sentence.

* Italicization: A formatting style used for emphasis, titles, foreign words, etc.

You can italicize a clause for emphasis, but that doesn't change its grammatical function.

Here are some examples:

* Regular Clause: _The cat sat on the mat._

* Italicized Clause: _The cat sat on the mat._ (This is just for emphasis)

Let me know if you have another question, or if you're thinking of something specific!