[withoutboats]

This is sort of the problem: its very natural to refer to that as a lifetime! In fact, more natural than the lifetime of a reference, because we intuitively think of variables as being "alive" and references as being short-term "views" of the variables.

As in the sibling comment, "scope" could be used, but indeed maybe we should have just called lifetimes "scopes" or something (though they are not lexical, whereas scopes are usually thought of as lexical pyramids).

I probably would just say lifetime usually, but I would be being imprecise and potentially unclear!

[oconnor663]

I propose that we refer to the (potentially non-lexical) scope of a variable as its "zone". Active variables would thus be said to be "in the zone".

[withoutboats]

This touches on some interesting history: lifetimes were originally (in other PL literature) called "regions" (MS Research's Verona also uses this terminology). Lifetime was chosen because an analogy to time seemed more intuitive for this concept than an analogy to space - space analogies being usually used for sections of program memory, rather than periods of program execution.