@Archie,
A simple example is in the basic lesson of Old Joe Clark in G… bar 35 - 38, where @BanjoBen actually has written Ending in the tab! You will also note the last 2 bars (37 - 38) is a variation of the “shave” ending… altered but still recognizable with the V - I cadence.
I do find it also interesting that these “endings” are typically 1/2 of the standard song phrases denoted as 1st A Part, 2nd A Part, 1st B Part and 2nd B Part… all being 8 bars in length.
So… As “Kickoff” is 1/2 phrase (4 bars) - so is the “Ending” (also 4 bars)… almost suggesting or implying that the two together balance out to be another full phrase (Kickoff + Ending = 8 bars)… to frame the song… but split on each side of the main song’s melody lines… at the beginning and end.
For me… That feeling and knowing the ending is approaching - having never heard a certain song before, is a cool part of Bluegrass. The listener often can feel the ending and participate with the band’s hard stop song conclusion. You can clearly notice how well this plays live by the timing of the audience’s applause, hoops and hollers. Contrast this with other songs that merely drag out and slow down the last 3 chords… Or just extend the final chord with a mini “Let’s go nuts” improv of notes and drum fills - cymbal crash. Or the classical symphonic endings with dramatic root chord repetitive counts and crescendos. It may seem subtle when you don’t think about it… but as a “music of the people”, this is another example of how Bluegrass has its’ own Mark and charm… distinctive and even celebrated by musicians with the audience/fans.
I considered “Outro”… But I think those are endings where a set of chords are repeated and faded… so not a suitable name as it doesn’t apply by that definition.
Maybe, “Ending” is simply good enough… although it seems so boring as compared with other song-part names like Kickoff, Part A, turnaround, and bridge.
Caboose? 
Nah - even though I like the train tie-in, it feels a little awkward or clunky.
Maybe, Close 4 (as “4-Close” would make people think their homes are being repossessed 
).
Or… To borrow from the tradition… “Shave 4” might work?
