The Hebrew noun reyach means a scent, smell, or aroma — pleasant or unpleasant. In sacrificial contexts it consistently describes the 'pleasing aroma' (reyach nichoach) of offerings made to God, signifying divine acceptance.
The phrase reyach nichoach ('pleasing aroma') appears over 40 times in Leviticus, Numbers, and Ezekiel in connection with burnt offerings and grain offerings. It is not that God needs food — it is the language of divine acceptance. After Noah's flood, the LORD 'smelled the pleasing aroma' and resolved never again to curse the ground (Genesis 8:21). This aroma language reaches its fullness in Ephesians 5:2, where Christ's sacrifice is described as 'a fragrant offering and sacrifice to God.'