A CPU is made up of many individual CPU cores. A CPU core is a physical component of the CPU hardware.
A thread (or hyperthread) is half of a CPU core, which competes for the time of the entire core. When both threads of a CPU are competing for resources, the performance of each thread can drop to about 60%. You can read this article that shows the thread performance, relative to the entire core. Mostly all of our competitors sell threads, because it allows them to sell the other thread on the same core to another customer. This overselling technique causes inconsistent performance, and allows companies to advertise "dedicated" threads. A "hyperthread" is never dedicated, because it does not have exclusive access to the CPU core.
A vCPU is a virtualized CPU core, thread, which does not neccessarily have a 1 to 1 ratio on the physical server. A physical server with 8 cores can run a VM with 200 vCPUs.
Slicie sells CPU cores. We don't sell threads because we find it confusing and dishonest.