Thanks for all the responses, and the link to the other thread. I'm starting to assume it's a type-o. The way she teaches, pivot bumps are all done with the forward foot resting on its ball next to the standing leg, and the forward hip is up on the 1. It can be stationary, can move forward (only), and rotate around in either direction.
Choo-choo, on the other hand, involves the forward foot moving slightly forward, then slightly back, with the associated hip bump. A single choo-choo is forward for one count with hip bump up, then foot back one count with associated hip bump. Double choo-choo is foot forward with two hip bumps, then foot back with two hip bumps. Plus, the arm positions are different.
What threw me for a loop is her list includes these four:
Choo-Choo
Pivot Bump with 3 variations
SIngle Choo-Choo
Double Choo-Choo
then she goes on from there. I'm thinking it's a double listing. Choo-choo can't be different from single choo-choo. . .

Okay, Ladies: I have been led down the path of clarity (and to the store for new index cards to replace all the wrong ones!) I'm sure there are regional variances on these names, but here in Santa Fe our terminology is as follows:
Choo-choo: weight on back slightly bent leg, forward leg glute contracts to move hip up on each count, forward foot on demi-point next to back foot. Stationary or moving forward.
Pivot Bump: Choo-choo that rotates around oneself. The three variants are the arm positions in relation to direction of turn.
Single choo-choo: Forward foot (meaning the foot stage front) moves toward toe of standing foot while you create one hip "bump", then moves toward heel of standing foot with one hip "bump" with specific arm position.
Double choo-choo: same as single but with two hip "bumps" front and two back with their specific arm positions.
Turns out my confusion was I was calling the pivot bump without moving (which I now know is a choo-choo) still a pivot bump. Since I then needed three variations of pivot bump, I decided those must be the stationary position, moving forward and rotating.
Of course if I'd been paying attention, I would have realized a stationary position wouldn't be called a "pivot" anything--same with moving forward. Oh well. I got an A for effort.
Now I look forward to having Carolena here in two weeks for workshops, to see what SHE calls everything! ;-P
Thanks again for everyone's input.

It's like any other language; we all speak English, which is preserved to large extent through the written form . . .but regionalities do creep in, along with accents. For instance, if you go to a restaurant here and order an enchilada, you might be asked if you want "Christmas." No, you tell the waiter, that's too long a wait, you're hungry now. But here, "christmas" also means you want half you enchilada covered in green chili, and half in red! :-P
Despite name changes, regional differences, etc., if each of you lovely ladies were to descend upon our local group, you'd all be able to dance together--THEREIN lies the true beauty of ATS. The form itself remains in tact; since you are following movement, not language in performing it, the bottom line is it's still the same. Choo-choo!!!!!

right!
this is what i had to that name www.youtube.com/watch

see, now, I woulda thought the first clip at 3:06 would be called doubles/double hip bumps.

I think I need clarification on what a double choo-choo is.