What is the "seed sequence" of a miRNA?

miRNAs regulate the gene expression by binding to the mRNA. The seed sequence is essential for the binding of the miRNA to the mRNA. The seed sequence or seed region is a conserved heptametrical sequence which is mostly situated at positions 2-7 from the miRNA 5´-end. Even though base pairing of miRNA and its target mRNA does not match perfect, the “seed sequence” has to be perfectly complementary.