Attribute of God expressing that He had no beginning and will have no end, i.e., He always was and always will be.
The very essence of God demands His existence, and that there never was a possibility of His not being.
Boetius defines eternity as the perennial, interminable, perfect possession of life in its fullest totality, always without beginning and without end.
There is no succession of anything, succession belongs to time.
God alone is eternal, there is in Him no past, no future, everything is the never beginning and never ending present.
New Catholic Dictionary