What is Gene Ontology and how is GO enrichment analysis performed?

Gene Ontology (GO) is a standardized vocabulary describing gene and protein functions across three domains: Biological Process (BP - what the gene does), Molecular Function (MF - biochemical activity), and Cellular Component (CC - where it functions). GO enrichment analysis tests whether specific GO terms are over-represented in a gene list compared to background. Methods include: hypergeometric/Fisher's exact test (for gene lists), GSEA (for ranked lists), and topGO (accounting for GO hierarchy). Multiple testing correction is essential due to many tests. Tools include DAVID, g:Profiler, clusterProfiler, and Enrichr. Results help interpret biological meaning of gene sets from experiments.