The definition of write-in, provided by the Free Online Dictionary. Most anarchists, and rightly so (to an extent), propose NOT VOTING as a means to further the cause. This strategy is despicably deficient. Why? A couple of reasons:
1. Voting, while useless, is voluntary. Even if you can convince your voting friends to adhere to the non-aggression principle, you will not EVER convince them not to vote in the name of such a notion. The chain of command between placing a slip of paper in a box and a police officer shooting a man for resisting taxation is too long and convoluted for anyone, anarchist or no, to seriously suggest that one morally implicates a person for the end consequence of the other.
2. By not voting, you open yourself to the classically fallacious (and first-amendment denying) "those who don't vote have no right to complain!". Since voting is done in secret, you can walk into that booth and vote for all the nobody you want. But hell, get creative. Vote everybody. Vote Jehovah. Vote Rowan Atkinson. Just as long as whoever it is will never accept the invitation.
3. We finally get to join the Get-Out-The-Vote campaign, only we get to have infinitely more fun doing it by asking questions like:
Does a not voting constitute a vote for nobody?
Does a vote for one person constitute a vote against another?
How many votes would it take to cross the threshold into supreme-court-ruling turning?
Is a voting multiple times, once for each candidate, for all candidates; voter fraud, one vote for everyone, or no vote at all?
4. Action is far more inspiring to a cause than non-action, no matter the action in question or how useless it may be. Ask any damn rally organizer or charity activist you want, you'll get the same answer - keep people doing easy shit symbolically for a hard cause practically, and you've won half the battle. By deliberately refraining to vote, you put yourself in the same class as those who routinely just don't give a shit, and your reasons for inaction could not be further apart. You don't vote for caring too much, they for caring too little.
5. Clog in the cogs, anyone? Voting for "Uncle Sam" is so much more time-consuming to vote counters than staying home and having him get elected anyway. Voting Nobody is active, spiteful, creatively de-constructive, and honest. What's not to love?
In conclusion, get out there and vote for your ruler - put your own name down if it really comes to it.