VPN is short for virtual private network. Many users probably know this from work, as many companies only allow remote access via VPN. But that is not what is meant here. You can easily set up your own VPN at home, completely free with FritzBox, for example.
But what you don't have are servers in different countries from which you can get foreign IP addresses. When you use a VPN service on your computer, smartphone, or tablet, it encrypts internet traffic from your devices to the VPN provider's servers. If you visit a website with a VPN turned on, you take a detour through the VPN provider and use its IP address.
This has several effects: Your data is protected by encryption, which is practical if you are using an open WiFi network in a hotel, for example. Since you're browsing using the VPN server's IP address and providers have servers in many different countries, you can elegantly change location and practically pretend you're in the USA or Switzerland, for example – and thus get around geo-blocked websites.
But there is also a big drawback: you have to trust the VPN provider because all your internet traffic goes through their server and they should not store or even resell any data about the sites you visit.
