Lévitique 3:9

And of the offering of his consecrated oblation he shall offer the best of its fat,, and remove the whole of the tail, close to the spine, the covering of fat which covereth the inwards, even all the fat that is upon the inwards.

its suet: the entire fat-tail This phrase is to be understood literally, for the fat-tail falls under the category of suet. Thus the Sadducees [a derogatory reference to Karaites — Translator] are in error, as I shall explain in the parasha of Ṣav [comment on 7:23]. Sa‘adya Gaon also erred in saying that the verse should read, “its suet, and the fat tail….” This interpretation violates Hebrew usage; if it were correct, Scripture should either have said “ its suet, and its fat-tail” or “ the suet, and the fat-tail”.

the spinal column This word is understood from its context, since it has no cognate. Some people derive it from the word “wood”, but that is far-fetched.

CHELBO’ (THE FAT THEREOF) ‘HA’ALYAH TH’MIMAH’ (THE FAT TAIL ENTIRE). The term cheilev (fat) in the Sacred Language indicates that part of the fat which is separate from the meat and not joined to it. Shuman, on the other hand, is that fat which is intertwined with the meat and cannot be separated from it, something like that which Scripture states: ‘Vayishman Yeshurun’ (But Jeshurun waxed fat); so they did eat, and were filled ‘vayashminu’ (and became fat); ‘hashmein’ (make fat) the heart of this people; and my flesh is lean ‘mishamen’ (and hath no fatness); and it shall be rich ‘v’shamein’ (and fat); my soul is satisfied as with marrow ‘vadeshen’ (and fatness),, but deshen. We must assume then that Ramban considered them equivalent terms. This is strengthened by an examination of the Hebrew wording of the verse: ‘k’mo cheilev vadeshen tisba nafshi.’ Now deshen is thus in parallelism to cheilev; hence deshen must here be understood as shuman, as explained above. and similarly in all places. But cheilev is the fat which is separate from the meat and covered by a membrane, and is easily peeled off. The Hebrew language never interchanges these terms [cheilev and shuman] in any place. Thus we say, basar shamen (fat meat), but not basar cheilev [since cheilev, as explained, is the fat which is separate and distinguished from the meat]. Similarly in languages of other nations these terms are separate. The term cheilev is sometimes used metaphorically, as is written, when ye set apart ‘chelbo’ (the best thereof) from it, since the good part of the produce which is taken up [to be given to the priest], Scripture figuratively calls cheilev, just as the cheilev is set apart in the offerings. ‘Cheilev kilyoth’ (the kidney-fat) of wheat — Scripture here compares wheat to the kidneys and the fat therein, just as it states, and of the blood of the grape thou drankest foaming wine, although wine is not blood [hence we must conclude that Scripture only uses these terms figuratively]. And ye shall eat the ‘cheilev’ (fat) of the land means that they shall eat the best of the bullocks, sheep, and goats and all animals. Such is the usage of this figure of speech.
Now the tail does not contain …

לעומת העצה, the kidneys; our sages in Chulin 11 describe how this tissue is to be removed.