As we’ve now seen, in the plainest terms immortality means “will live forever” and conditional means “subject to a condition.” Narrowly expressed, that’s primarily what we mean by the words conditional immortality. There is more involved theologically, but at the level of words, it remains for us to appreciate the secondary sense of conditional that we are also invoking.
A second sense of conditional, denying universal and absolute
In theological labeling convention, conditional is a technical term implying that conditions will not be universally met (i.e. rendered absolute). The reason for this is that it’s not merely the fact of a condition that is in view, but rather the interesting question of scope. If you wanted to announce a universal scope, you would call your position universal or unconditional. If you wanted to refer to a limited, nonuniversal scope, you would refer instead to “conditional” matters. In this sense, something can’t be both universal and conditional.