chore: reword

Author: jo-mueller

index.md

@@ -564,7 +564,7 @@ to do so by estimating the transformations' inverse if they choose to.
 
 **Transformations in array coordinate units**:
 Some applications might prefer to define points, regions-of-interest or transformation parameters
-in array coordinates rather than physical units.
+in array coordinates (also referred to as pixel coordinates) rather than physical units.
 Because transformations are agnostic to whether they refer to array or physical coordinates,
 indicating that choice explicitly will be important for interoperability.
 This can be expressed in the metadata in multiple ways, including: