term:

Perpetuity

perpetuity n

pl: -ties
1 : the quality, state, or duration of being perpetual [devised to them in ]
2 a : the condition of a future estate limited in such a way as not to vest within the period fixed by law for the vesting of an estate
;also
: a limitation that gives rise to such a situation
b : an estate that will not vest within the period fixed by law see also rule against perpetuities, statutory rule against perpetuities
3 : an annuity payable forever