The licensing system in vSphere uses specific terminology and definitions to refer to different licensing-related objects.

License Key
A license key encodes details about the product it is associated with, the license expiration date, the license capacity, and other information. The license key is assigned to an object to activate the functionality of its associated product.
A container for a license key of a VMware product. To use a license key, you create a license object in the vSphere Web Client or the vSphere Client, and insert the license key into the license. After the license is created, you can assign it to assets.
Product Edition
A set of specific features that are associated with a unique license key. When assigned, the license key unlocks the features in the product edition. Examples of product editions are vSphere Enterprise Plus, vSphere Standard, vCenter Server Essentials, VMware vSphere Platinum, and so on.
Enabled or disabled functionality by a license that is associated with a specific product edition. Examples of features are vSphere DRS, vSphere vMotion, and vSphere High Availability.

A product that is packed and distributed independently from vSphere. You install a solution in vSphere to take advantage of certain functionality. Every solution has a licensing model specific for the solution, but uses the License Service for license management and reporting. Examples of solutions are VMware Site Recovery Manager, vRealize Operations Manager, vCloud Network and Security, and so on.

Any object in vSphere that requires licensing. If the license has sufficient capacity, the license administrator in vSphere can assign one license to one or multiple assets of the same type. Suite licenses can be assigned to all assets that are part of the suite. Assets are vCenter Server systems, ESXi hosts, and products that integrate with vSphere such as VMware Site Recovery Manager, vRealize Operations Manager, and others.
License Capacity
The number of units that you can assign to assets. The units of a license capacity can be of different types depending on the product that the license is associated with. For example, a license for vCenter Server determines the number of vCenter Server systems that you can license.
License use
The number of units that an asset uses from the capacity of a license. For example, if you assign a per-virtual-machine license to VMware Site Recovery Manager, the license use for VMware Site Recovery Manager is the number of protected virtual machines.