Understanding Instance Data and Metadata
There are two types of activity properties: meta properties and instance properties. A meta property is immutable at run time, so the property must be set to a literal value at design time. An instance property can be set at design time, or the property can be bound to instance data, in which case the actual value is not determined until run time. Instance properties can also be modified directly during workflow execution.
Metadata is related to activities in the same way that attributes are related to .NET Framework classes. Metadata is only configurable at design time and, once an activity is built, cannot be changed. For example, System.Workflow.ComponentModel.Activity.Name is metadata because the name of an activity in a workflow's tree is part of the definition of the workflow.
Instance data, on the other hand, maps to properties and fields on classes. These can be modified at run time. One example is the Error string on the SuspendActivity, which does not have to be defined at design time, but instead can be changed right up until the activity runs.