Apropos of is a term used to discuss or refer to a related topic or issue. There are several synonyms for this term, such as with regard to, concerning, regarding, as for, and talking about. Each of these phrases is interchangeable with apropos of and can be used to introduce a related subject. With regard to is a formal way of transitioning to a related topic, while talking about is more informal and commonly used in casual conversations. Meanwhile, as for is often used to introduce a different perspective or opinion on a particular matter. Regardless of the synonym used, the intended meaning of introducing a related topic or issue remains the same.