The Resource Initials fields list the abbreviations for the names of resources.
There are two categories of Resource Initials fields.
Data Type Text List (text list field: A type of field whose content is a list of text items separated by the list separator character, typically a comma. Examples include the Resource Group and Resource Names fields.)
Resource Initials (task field)
Entry Type Calculated (calculated field: A field in which the value is determined by Project based on information in other fields. Project may recalculate the value automatically or when you specify, depending on your choice of calculation settings.)
How Calculated Microsoft Office Project builds the list of resource initials from the contents of the Initials field for all resources in the project.
Best Uses Add the Resource Initials field to a task sheet when you want to display or filter the initials for resource names.
Example You want to review the assigned resources for tasks in the Gantt Chart view. To be able to review the task names, resources, and other information, you add the Resource Initials field to the sheet portion of the Gantt Chart view.
Resource Initials (assignment field)
How Calculated The content of the Resource Initials field for assignments is equivalent to the Initials field for resources.
Best Uses Add the Resource Initials field to the timephased portion of the Task Usage view when you want to display or filter the initials for resource names. This field is available only in the Task Usage view.
Example You want to conserve space in the timephased portion of the Task Usage view. You replace the Resource Names field with the Resource Initials field.