The vow-offering appears to have been a peace-offering vowed upon a certain condition; the voluntary-offering, one offered as the simple tribute of a devout heart rejoicing in peace with God and man offered on no external occasion (compare Leviticus 22:17-25).
Related Commentaries of Leviticus 7:16
Leviticus 7:16
16 But if the sacrifice of his offering be a vow, or a voluntary offering, it shall be eaten the same day that he offereth his sacrifice: and on the morrow also the remainder of it shall be eaten: