A public subnet has a route to an Internet Gateway, so instances can be reached from the internet (with correct firewall rules). A private subnet has no direct inbound internet route; it’s commonly used for app servers and databases. Often the load balancer is public, while app/DB stay private.
Expanding on the short answer — what usually matters in practice:
A tiny example (an explanation template):
// Example: discuss trade-offs for "public-vs-private-subnet:-what-is-the-difference"
function explain() {
// Start from the core idea:
// A public subnet has a route to an Internet Gateway, so instances can be reached from the i
}