A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service. The virtual dedicated server (VDS) also has a similar meaning.
A VPS runs its own copy of an operating system (OS), and customers may have superuser-level access to that operating system instance, so they can install almost any software that runs on that OS. For many purposes they are functionally equivalent to a dedicated physical server, and being software-defined, are able to be much more easily created and configured. They are priced much lower than an equivalent physical server. However, as they share the underlying physical hardware with other VPSes, performance may be lower, depending on the workload of any other executing virtual machines.
Many people don’t switch to a VPS because they don’t know how to manage it. They don’t have Linux systems administration skills and they do not have an idea about terminal access, SSH and shell commands. The number of such people is really high. That is why hosting companies now offer managed vps hosting. That type of hosting allows such people not to worry about the technical stuff and focus on their business. Their hosting company will manage the vps for them.
A managed vps is a server that is installed, configured, secured, updates, audited by an expert. The experts doing that job are called systems administrators. The biggest web hosting companies have plenty of them to be able to manage thousands of servers. A VPS requires to be updated regularly in order to be secure.