2 Answers

If you don't vote in Australia, you'd get a fat fine in the next mail.

If by voting you mean a voter casting a ballot - an "abstention" vote would be not filling out (or electronically or mechanically indicating or selecting) any candidate, bond issue, proposition or appointment by marking the ballot, but then casting the vote (mechanically or by drop box or other means) making it a legally cast ballot, but one containing no countable votes. One may abstain in rendering a judicial decision (even in a one-judge panel). In the US, in the Houses of Congress, a congressional member may abstain from voting yea or nay on any bill, calendar vote, impeachment article and so forth. This is also true in the 50 state government legislatures as well. So the "answer" would be ... it depends on which "voting system" you're talking about and semantically what your intended meaning and definition of abstention is. How's that  for "abstaining" from a direct answer? :)