Update next/image docs for width & height

docs/api-reference/next/image.md

@@ -48,15 +48,27 @@ When using an external URL, you must add it to
 
 ### width
 
-The width of the image, in pixels. Must be an integer without a unit.
+The width of the image. Must be an integer without a unit.
 
-Required, except for statically imported images, or those with [`layout="fill"`](#layout).
+The meaning of the `width` property can change depending on the [`layout`](#layout) and [`sizes`](#sizes) properties since some layouts will stretch to fill the parent container and others will not.
+
+The `width` property represents the _rendered_ width in pixels when `layout="intrinsic"`, `layout="fixed"`, or `layout="raw"` without `sizes` so it will affect how large the image appears.
+
+The `width` property represents the _original_ width in pixels when `layout="responsive"`, `layout="fill"`, or `layout="raw"` with `sizes` so it will only affect the aspect ratio.
+
+Required, except for [statically imported images](#local-images), or those with `layout="fill"`.
 
 ### height
 
-The height of the image, in pixels. Must be an integer without a unit.
+The height of the image. Must be an integer without a unit.
+
+The meaning of the `height` property can change depending on the [`layout`](#layout) and [`sizes`](#sizes) properties since some layouts will stretch to fill the parent container and others will not.
+
+The `height` property represents the _rendered_ height in pixels when `layout="intrinsic"`, `layout="fixed"`, or `layout="raw"` without `sizes` so it will affect how large the image appears.
+
+The `height` property represents the _original_ height in pixels when `layout="responsive"`, `layout="fill"`, or `layout="raw"` with `sizes` so it will only affect the aspect ratio.
 
-Required, except for statically imported images, or those with [`layout="fill"`](#layout).
+Required, except for [statically imported images](#local-images), or those with `layout="fill"`.
 
 ## Optional Props