One is simple "Choose vote"
in which you specify a list of submissions and every PC member needs to
choose some number of them. For example, "Choose up to three of the
submissions in 'Maybe Reject' category to move back to the 'Discuss' pile."
The other type is a "Grade vote" in which you specify a list of submissions
and every PC member needs to grade these submissions on some scale. For
example, "Grade each of the remaining submissions in the 'Discuss' category
on a scale of zero to three."
(Technically, a "Choose vote" is a special case of a "Grade vote"
with the scale being 0-1, but the interface that the PC member sees for
a "Choose vote" is slightly simpler than for a "Grade vote".)
In either type of vote, the tally is the sum of votes that each submission
received. (In the "Choose vote" this is the number of PC members that chose
that submission.)