Albert Barnes Commentary Leviticus 7:16

"But if the sacrifice of his oblation be a vow, or a freewill-offering, it shall be eaten on the day that he offereth his sacrifice; and on the morrow that which remaineth of it shall be eaten:" — Leviticus 7:16 (ASV)

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 .