A BAM file is a binary format used to store aligned sequence data, typically produced by mapping raw reads against a reference genome. It is a compressed version of the Sequence Alignment/Map (SAM) format, designed to efficiently store large amounts of alignment data and allow rapid access to specific regions within a genome. BAM files include information such as the read sequences, mapping quality scores, CIGAR strings (representing alignment operations), and flags indicating the read's alignment status. They are widely used in downstream analysis for variant calling, visualization, and quality assessment of sequencing experiments.