Some more comments

Assets/Scripts/TerrainGeneration/TerrainGenThread.cs

@@ -21,6 +21,12 @@ public class TerrainGenThread
         TerrainData = data;
     }
 
+    /// <summary>
+    /// Gets the generated heights.
+    /// Throws InvalidOperationExcepion if the heights
+    /// aren't built yet.
+    /// </summary>
+    /// <returns></returns>
     public float[,] GetHeights()
     {
         if (ready)

Assets/Scripts/TerrainGeneration/TerrainGenerator.cs

@@ -51,7 +51,12 @@ public class TerrainGenerator : MonoBehaviour
 
     private List<TerrainGenThread> generators = new();
 
-    private void ThreadGenerationFinished(TerrainGenThread genThread)
+    /// <summary>
+    /// Apply the terrain that was generated by genThread.
+    /// </summary>
+    /// <param name="genThread">The terrain gen thread that has finished 
+    /// generating its terrain heights.</param>
+    private void ApplyGeneratedTerrain(TerrainGenThread genThread)
     {
         genThread.TerrainData.SetHeights(0, 0, genThread.GetHeights());
 
@@ -96,6 +101,10 @@ public class TerrainGenerator : MonoBehaviour
         StartCoroutine(CheckThreads());
     }
 
+    /// <summary>
+    /// Wait until all threads are done.
+    /// </summary>
+    /// <returns></returns>
     private IEnumerator CheckThreads()
     {
         yield return new WaitForEndOfFrame();
@@ -121,7 +130,7 @@ public class TerrainGenerator : MonoBehaviour
         {
             if (genThread != null)
             {
-                ThreadGenerationFinished(genThread);
+                ApplyGeneratedTerrain(genThread);
                 yield return new WaitForEndOfFrame();
             }
         }