Is there a Buda and a Pest?

Excuse me, could you please clarify something for me? I've come across the phrase "Buda and Pest" and I'm wondering if there's actually a Buda and a Pest, or if it's a figure of speech. Is it referring to two distinct entities, or is it simply a way to describe something? And if there are indeed two entities, could you elaborate on what they are and how they relate to each other? I'm quite intrigued and would love to learn more about this.