Update site/docs/relations/physical_relations.md

Co-authored-by: Weston Pace <[email protected]>

site/docs/relations/physical_relations.md

@@ -222,7 +222,7 @@ The expand operation creates duplicates of input records based on the Expand Fie
 | Property  | Description                          | Required |
 | --------- |--------------------------------------| -------- |
 | Input     | The relational input.                | Required |
-| Direct Fields | Expressions describing the output fields.  These refer to the schema of the input.  Each Direct Field must be a Consistent Field or a Switching Field  | Required |
+| Direct Fields | Expressions describing the output fields.  These refer to the schema of the input.  Each Direct Field must be an expression or a Switching Field  | Required |
 
 ### Switching Field Properties