I have seen mostly two definitions for a "viable character":
- Unlikely to die in the first few encounters
- Not much weaker than the strongest possible character of similar build
Is there an accepted definition for this term on the site?
It doesn't really matter what the stack-at-large thinks it means for a character build to be viable. Instead of using the word viable, just present a well defined problem to solve. "Is this character build viable" is not a well defined problem to solve, but it's fine as a question title, as long as you explain what you mean in the question body. It doesn't matter what we think viable means, it matters that you tell us what it means to you so we can work toward that in our solutions.
Viable is dependent on lots of factors.
Questions of viability need to define what viable is for the group and game:
Note that game here is not to be automatically put equal with the system, but the two can overlap: a game of Werewolf could focus on inter-clan intrigue and mysticism, it could be eco-terrorism or it could be a courtroom drama with Werewolf-lawyers and -PIs fighting Pentax on the bench.
Problems with "Unlikely to die":
Problems with "Significantly weaker than possible":
Most modern combat oriented RPGs1 have encounter design guidelines; if another character comes, add a monster of level X.
This is your measuring rod, your measuring rod. The character is viable if it is stronger than the monster that it causes to appear. Otherwise the party is stronger (compared to the opposition) if the player stays at home.