A pose file.
If you save it without morph channels - it is a POS pose
(position)
If you save it with morph channels - it is a MOR pose
(morph) - it also has position
This is stuff Poser does automatically

You save a face pose - this is automatically a MOR pose for the head only - but no position

The thing is - you do an expression face Wide Grin or something - You use a standard V1 to do it - if this is used on a character formed by setting dials, the V1 dial part gets erased, and if the expression was saved using a V2 head, the whole character gets erased. When Poser saves it, it saves settings for all the morphs, even if the setting is zero.
If you want to use characters set up by morph dials and do not want the protect them by Spawning a combined morph for it, the only safe way to use expressions:
save the expression poses to the library with a figure that ONLY HAS expression morphs in it - no construction morphs.
If a morph is not in the CR2 a posed is saved from, Poser will not save a setting for it.

You will find instances where an expression was saved from a character also set with morph dials, and not only do you get the expression, you get the character. a bass ackwards way of doing it.

.

Dan Wilmes is working on making this transparent in CR2Edit.
You either pay to have it done for you by a program.
or
You learn how for yourself.
or
You don't play.