What is on-demand revalidation in Next.js, and how is it different from time based revalidation?

Time based revalidation refreshes cached content automatically after a set number of seconds, while on-demand revalidation lets you manually trigger a cache refresh at the exact moment your content actually changes, such as right after publishing a new blog post, giving you precise control over when fresh data appears.

// Time based: refreshes automatically every 60 seconds
fetch(url, { next: { revalidate: 60 } });

// On-demand: refreshes only when you trigger it
revalidatePath('/blog');