A template field view is a visual representation of a template field in SitecoreUML syntax, as displayed on the diagrams generated as part of the SitecoreDXG output.
In SitecoreUML diagrams, Template Field Views are displayed as child line-items of a template view, in the syntax
For those users who also use SitecoreUML as a tool for writing/modifying template architectures, you may be used to typing abbreviations for the field types, e.g. "SLT" or "SingleLineText" for "Single-Line Text". If you deploy your changes to Sitecore and then use SitecoreDXG to generate the documentation for the solution then your abbreviations will automatically be expanded to the full field type name (e.g. "Single-Line Text").
For more details, refer to the SitecoreUML documentation.