diff --git a/Docs/Architecture/12_glossary.md b/Docs/Architecture/12_glossary.md
index b04895b..a428340 100644
--- a/Docs/Architecture/12_glossary.md
+++ b/Docs/Architecture/12_glossary.md
@@ -3,6 +3,7 @@
 | Term | Definition |
 | --- | --- |
 | Blosm | Blender add-on (2.7.28) that imports OSM data as 3D building and street blockouts. Used for layout only — not authoritative for façade or height. |
+| PIE | Play In Editor — an Unreal Editor feature that runs the current map as a live game session inside the editor window, with full game code, input, and physics, without packaging a build. Used for interactive verification (walk, reset, pause) before the scripted QA self-test. |
 | Complex-as-simple collision | `CTF_UseComplexAsSimple`: Unreal collision mode where the render mesh triangles are used as the collision surface, instead of a simplified proxy. Required for terrain so the player walks on the actual ground shape. |
 | DEM | Digital Elevation Model. 3DEP 1 m resolution GeoTIFF covering the demo bounds. Source of terrain heightfield. |
 | El Capitan | El Capitan Entertainment Centre, 6838 Hollywood Blvd. The hero building of the demo. |
@@ -16,5 +17,6 @@
 | Site | The terrain, road, sidewalks, kerbs, and crossing markings — the ground-level infrastructure of the demo area. |
 | Squash merge | Git merge strategy that compresses all branch commits into one commit on `main`, keeping a linear history. |
 | Swept transect | A QA technique that raycasts vertically at regular intervals along a path (e.g. every 200 cm along both sidewalks and the carriageway) and counts holes (misses). Zero holes = the block is fully walkable. |
-| World Partition | Unreal’s world composition system for large open-world levels. Not yet used in `0.1.0` but planned for `0.3.0+` driving routes. |
+| UE | Unreal Engine — Epic Games' real-time 3D creation platform (version 5.8.4 in this project). Comprises the Unreal Editor (including PIE, content browser, viewport, blueprint editor), a C++ game framework, and runtime systems for rendering (Vulkan RHI on Linux), physics (Chaos), and input (Enhanced Input). The game project is `GigLine.uproject`; game code is a single C++ module in `Game/GigLine/Source/GigLine/`. |
+| World Partition | Unreal's world composition system for large open-world levels. Not yet used in `0.1.0` but planned for `0.3.0+` driving routes. |
 | Y convention | In Unreal, south = +Y, north = −Y (confirmed from street mesh orientation). In Blender, north = +Y; the `ue_metric_v1` export preset flips Y. |
diff --git a/Docs/Architecture/architecture.md b/Docs/Architecture/architecture.md
index 3180e14..585f4af 100644
--- a/Docs/Architecture/architecture.md
+++ b/Docs/Architecture/architecture.md
@@ -490,6 +490,7 @@ Rule: place a building only against a neighbour or street mesh, never in isolati
 | Term | Definition |
 | --- | --- |
 | Blosm | Blender add-on (2.7.28) that imports OSM data as 3D building and street blockouts. Used for layout only — not authoritative for façade or height. |
+| PIE | Play In Editor — an Unreal Editor feature that runs the current map as a live game session inside the editor window, with full game code, input, and physics, without packaging a build. Used for interactive verification (walk, reset, pause) before the scripted QA self-test. |
 | Complex-as-simple collision | `CTF_UseComplexAsSimple`: Unreal collision mode where the render mesh triangles are used as the collision surface, instead of a simplified proxy. Required for terrain so the player walks on the actual ground shape. |
 | DEM | Digital Elevation Model. 3DEP 1 m resolution GeoTIFF covering the demo bounds. Source of terrain heightfield. |
 | El Capitan | El Capitan Entertainment Centre, 6838 Hollywood Blvd. The hero building of the demo. |
@@ -503,7 +504,8 @@ Rule: place a building only against a neighbour or street mesh, never in isolati
 | Site | The terrain, road, sidewalks, kerbs, and crossing markings — the ground-level infrastructure of the demo area. |
 | Squash merge | Git merge strategy that compresses all branch commits into one commit on `main`, keeping a linear history. |
 | Swept transect | A QA technique that raycasts vertically at regular intervals along a path (e.g. every 200 cm along both sidewalks and the carriageway) and counts holes (misses). Zero holes = the block is fully walkable. |
-| World Partition | Unreal’s world composition system for large open-world levels. Not yet used in `0.1.0` but planned for `0.3.0+` driving routes. |
+| UE | Unreal Engine — Epic Games' real-time 3D creation platform (version 5.8.4 in this project). Comprises the Unreal Editor (including PIE, content browser, viewport, blueprint editor), a C++ game framework, and runtime systems for rendering (Vulkan RHI on Linux), physics (Chaos), and input (Enhanced Input). The game project is `GigLine.uproject`; game code is a single C++ module in `Game/GigLine/Source/GigLine/`. |
+| World Partition | Unreal's world composition system for large open-world levels. Not yet used in `0.1.0` but planned for `0.3.0+` driving routes. |
 | Y convention | In Unreal, south = +Y, north = −Y (confirmed from street mesh orientation). In Blender, north = +Y; the `ue_metric_v1` export preset flips Y. |
 
 ---