Tasks represent system activities that do not complete immediately, such as migrating a virtual machine. They are initiated by high-level activities that you perform with the vSphere Client in real time and activities that you schedule to occur at a later time or on a recurring basis.
For example, powering off a virtual machine is a task. You can perform this task manually every evening, or you can set up a scheduled task to power off the virtual machine every evening for you.
The functionality available in the vSphere Client depends on whether the vSphere Client is connected to a vCenter Server system or an ESXi host. Unless indicated, the process, task, or description applies to both kinds of vSphere Client connections. When the vSphere Client is connected to an ESXi host, the Tasks option is not available; however, you can view recent tasks in the Status Bar at the bottom of the vSphere Client.