ISR lets you serve a statically generated page but revalidate it in the background after a set interval. Users get cached content fast, and when it’s stale Next.js regenerates the page without a full redeploy. Use it for mostly static pages with occasional updates.
Expanding on the short answer — what usually matters in practice:
A tiny example (an explanation template):
// Example: discuss trade-offs for "what-is-incremental-static-regeneration-(isr)-an"
function explain() {
// Start from the core idea:
// ISR lets you statically generate pages and revalidate them in the background after a time
}