STAR (Spliced Transcripts Alignment to a Reference) is a powerful tool used in RNA-seq analysis. It's an alignment tool designed specifically for efficiently handling RNA-seq data. It works by aligning the RNA-seq reads to the genome, accounting for the splicing of the RNA. This allows it to accurately map reads that span intron-exon boundaries, which other alignment tools might struggle with. The resulting alignment can then be used for various downstream analyses, such as differential gene expression analysis or variant calling.