Say a governor vetoes a bill and to override the veto both chambers must gain 3/5s of the vote. Say the House votes 83-53 with 1 abstaining and 4 absent. Simply, does that 3/5s mean the entire chamber or just the ones who actually vote yea/nea? Are the abstainers and absent voters included in that supermajority? Would the House need 85 votes or 82 votes if 1 abstains and 4 are absent?
This would depend on exactly what rules were embedded the the state’s constitution.
You can have an unqualified or simple vote in which 60% of those voting yes or no must vote yes (absents and abstains do not count except the latter count for having a quorum present).
An absolute vote requires 60% of the members so absent and abstain count no on the override.
You also hear phrases like 3/5 of those present and voting (which would count abstains as not to override but not count absent).
I believe all states use the simple vote as does the federal government, but I don’t have a cite for that.
It’s up to each state to decide. This sideways table (PDF) shows the rules for each state. It looks like most states use the whole chamber but a few do only count the members who are present. (A few also allow a simple majority to override a veto.)
I was especially interested in Nebraska whose one-house legislature overrode by 30-19 the bill abolishing the death penalty. The chart showed that Nebraska requires 3/5 of all elected members to override, so Nebraska cannot have more than 50 legislators.
Incidentally, on a Windows computer you can turn the chart right-side up by pressing Ctl-Alt-arrow key (I forget which one, right or left depending on which way it is facing). I just learned it from another doper a couple weeks ago. First time I used it, except to test.