This is going to be boring but, if you think you might apply the terms distal or proximal to a rarity description please read on. Yesterday I was re-reading an ID article within which the term distal had been used in an 'interesting' fashion at least twice (by 'interesting' I mean unclear or incorrect, I'm not trying to alleviate the tedious nature of this post, an impossible task I think we can all agree). Within a discussion of tail bars, the author had used distal in a situation where 'sub-terminal' would have been much clearer and, later, with regard to a bar partly obscured by the uppertail coverts (presumably a typo in lieu of proximal). Therefore, in the spirit of universal education and due to the fact I am a birding pedant living in Gwent (where it is much easier to sit in reading about good birds rather than getting out and finding them) I present Dictionary Corner,... [insert fanfare here]
In the context of anatomical description, the term distal describes that end of a limb or appendage furthest from the point of attachment with the body; proximal describes the end of the limb or appendage that joins the body. The terms can, of course, be used in a relative manner to indicate where a structure lies along the proximodistal axis, e.g. a sub-terminal tail bar is distal in relation to almost every other part of the tail except the terminal bar (or perhaps tail-tip) to which it is proximal. If you are still struggling, if you imagine a central point within the bird then that end of the bill, tail, tarsus, etc., closer to this point is proximal, that which is further away is distal. Or, to put it another way if there's a bright centre to the birding universe, I'm sat in the county most distal to it.
There, now aren't we all going to sleep that much better in our beds tonight? Hmmm? Aren't we? Hmmm? Zzzzzzzz.