Is deprecated word the only difference between fill_parent and match_parent

As you said they are exact the same. As Romain Guy said, they have changed the name because "fill_parent" was confusing for developers. As matter of the fact, "fill_parent" does not fill the remaining space (for that you use the weight attribute) but it takes as much space as its layout parent. That's why the new name is "match_parent".

According to Romain Guy in this video, these words mark the same behaviour. But many developers misunderstood what fill_parent meant, hence they came up with an alias.

I have developed in Android long enough to also realize that there seems to be no difference except when you want to run on an older API. I would use fill_parent because I make all of my apps with minimum API 7. Also, on a side note, since Android is forward compatible this is the way to go.

Addition to the existing answers. Here is a part of the source code from LayoutParams class, both FILL_PARENT and MATCH_PARENT constants map to the same value. So we have absolutely the same functionality.

    public static class LayoutParams {
    /**
     * Special value for the height or width requested by a View.
     * FILL_PARENT means that the view wants to be as big as its parent,
     * minus the parent's padding, if any. This value is deprecated
     * starting in API Level 8 and replaced by {@link #MATCH_PARENT}.
     */
    @SuppressWarnings({"UnusedDeclaration"})
    @Deprecated
    public static final int FILL_PARENT = -1;

    /**
     * Special value for the height or width requested by a View.
     * MATCH_PARENT means that the view wants to be as big as its parent,
     * minus the parent's padding, if any. Introduced in API Level 8.
     */
    public static final int MATCH_PARENT = -1;
    ...