a gift handed over to God at the altar: the technical priestly term for what is presented to him as his portion
This is a specialized worship word, used almost entirely in the laws of Leviticus and Numbers and only a handful of times anywhere else. It names a particular class of what the people bring to God at the sanctuary: the portion that becomes his.
For centuries it was rendered "fire offering" or "offering made by fire," on the assumption that it was built from the ordinary word for fire and meant whatever was burned on the altar. Most scholars now think that reading does not fit the evidence. The same word is used for gifts that are never burned at all (the wine poured out as a drink offering, the bread of the presence that the priests eat, the breast and thigh of a fellowship offering that go to the priests as their share), and it is withheld from at least one offering that clearly is burned. So the term does not track "what goes into the flames"; it tracks "what is given over to God," some of which rises to him as smoke and some of which he passes on to his priests.
From there the meaning is steady across every passage. Whether the gift is burned whole, partly burned, poured out, or set aside for the priests to eat, it is one thing: a present formally transferred to God. Modern translations capture this with "food offering" or "food gift," picking up the related description of the offerings as "the food of God." The picture is less an altar as a furnace and more a table at which God is hosted with a gift.