Sequence similarity, identity, and homology are fundamental concepts in bioinformatics and biostatistics that describe the relationships between biological sequences, such as DNA, RNA, or proteins, but they are often misunderstood or used interchangeably, despite their distinct meanings. Understanding these distinctions is crucial for sequence analysis, evolutionary studies, and functional annotation. Sequence identity refers to the exact match of nucleotides in DNA or amino acids in protein sequences when two sequences are aligned. It is a straightforward measure that quantifies the percentage of positions in an alignment where the residues are identical. For example, if two protein sequences of 100 amino acids each have 85 positions with exactly the same amino acid, the sequence identity is 85%. Identity does not consider the physicochemical properties of residues; it only counts exact matches. High sequence identity often suggests functional similarity, but it alone cannot