public static final int padding
Since: API Level 1
Sets the padding, in pixels, of all four edges. Padding is defined as space between the edges of the view and the view's content. A views size will include it's padding. If a background is provided, the padding will initially be set to that (0 if the drawable does not have padding). Explicitly setting a padding value will override the corresponding padding found in the background.

Must be a dimension value, which is a floating point number appended with a unit such as "14.5sp". Available units are: px (pixels), dp (density-independent pixels), sp (scaled pixels based on preferred font size), in (inches), mm (millimeters).

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form " [package:][type:]name") containing a value of this type.

Constant Value: 16842965 (0x010100d5)
再看margin，以marginBottom 举例
android:layout_marginBottom
Since: API Level
Specifies extra space on the bottom side of this view. This space is outside this view's bounds.

Must be a dimension value, which is a floating point number appended with a unit such as "14.5sp". Available units are: px (pixels), dp (density-independent pixels), sp (scaled pixels based on preferred font size), in (inches), mm (millimeters).

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form " [package:][type:]name") containing a value of this type.

This corresponds to the global attribute resource symbol layout_marginBottom.

Related Methods
setMargins(int,int,int,int)
所以padding是定义控件自己的内容和控件边缘之间的距离，padding有填充填料的意思，而margin是在说控件的四个边缘之外的距离，指的是和别的控件之间的距离，margin有边缘，页面留白的意思

借用一幅别人的图来说明