Azure virtual machine size overview
Virtual machine size basically defines the amount of resources it could consume. The machine size defines the number of CPU cores, memory size, temporary disk size, etc. The size of the virtual machine can be changed anytime, even after the machine is deployed.
The cost of the size may change within different locations/regions. A region is the geographic area grouping data centers in that location. It gives users the ability to run applications where needed.
Find more information on the Microsoft website: