WHAT: Turborepo monorepo build system - caching, task pipelines, and parallel execution for JS/TS projects. WHEN: User configures turbo.json, creates packages, sets up monorepo, shares code between apps, runs --affected builds, debugs cache misses, or has apps/packages directories. KEYWORDS: turborepo, turbo.json, monorepo, dependsOn, task pipeline, caching, remote cache, --filter, --affected, packages, workspace, pnpm workspace, npm workspace, build optimization