Answer:
The two terms are often used for the same action.
The "pocket veto" is when a President (or other executive where applicable) simply holds a bill without signing it, so that Congress adjourns before the bill can be returned (as vetoed). This may be called an "automatic veto", because it requires no action on the President's part. It is similarly referred to as an "indirect veto" because no actual veto statement takes place. It is also an "absolute veto", or intended to be, because the Congress cannot vote to override it and pass the bill.
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