What is the exclusionary rule in the context of a police search?

^2. The contours of the exclusionary rule are well known: If challenged police conduct is shown to violate the Fourth Amendment "'the exclusionary rule requires that all evidence obtained as a result of such conduct be suppressed[,]... [including] not only what was seized in the course of the unlawful conduct itself the so-called "primary" evidence [citations]--but also what was subsequently obtained through the information gained...--the so-called "derivative" or "secondary" evidence [citations]. Thus, the "fruit of the poisonous tree," as well as the tree itself, must be excluded.'" (People v. Mayfield(1997) 14 Cal.4th 668, 760.)