Instance types offered by all providers.
Providers organize their products into multiple lines of servers aka instance types. Many decide to have three instance types: "General Purpose", "Compute Optimized" and "Memory Optimized". The differentiator between these types is often the amount of RAM per vCPU. Other providers prefer to split their server line by CPU type or by shared/dedicated CPU.
In most cases, each instance type has a fixed amount of RAM and a fixed price per vCPU.