What is a CDN and do you need one?
The short answer
A CDN (content delivery network) places copies of your site on servers worldwide. Each visitor then loads your site from a server nearby. That makes it faster and helps absorb traffic spikes. With international visitors a CDN is near-essential, and for a strictly local audience it is optional.
In detail
Without a CDN every visitor loads your site from the one server where it is hosted. For a visitor on another continent that means a noticeably slower visit. A CDN copies your static files to dozens of locations worldwide. Think of images, scripts and stylesheets. Each visitor is then served from the nearest point.
A CDN also takes load off your server. Most requests never reach your hosting anymore. That helps during traffic spikes and forms a first shield against denial-of-service attacks. Cloudflare is the best-known name. Its free tier is enough for most sites.
More and more hosts include one. Kinsta ships Cloudflare integration as standard. WP Engine bundles a CDN with every plan, and SiteGround has its own built in. If your audience is in one country, a fast server nearby does half the work. The CDN is then the finishing touch.