As we all know, much of the evaluation of scientists for various important career purposes involves the record of published work.
More is better.
We also know that, at any given point in time, one might have work that will eventually be published that is not, quiiiiiite, actually published. And one would like to gain credit for such work.
This is most important when you have relatively few papers of "X" quality and this next bit of work will satisfy the "X" demand.
This can mean first-author papers, papers from a given training stint (like a 3-5 yr postdoc) or the first paper(s) from a new Asst Professor's lab. It may mean papers associated with a particular grant award or papers conducted in collaboration with a specific set of co-authors. It could mean the first paper(s) associated with a new research direction for the author.
Consequently, we wish to list items that are not-yet-papers in a way that implies they are inevitably going to be real papers. Published papers.
The problem is that of vaporware. Listing paper titles and authors with an indication that it is "in preparation" is the easiest thing in the world. I must have a half-dozen (10?) projects at various stages of completion that are in preparation for publication. Not all of these are going to be published papers and so it would be wrong for me to pretend that they were.
Hardliners, and the NIH biosketch rules, insist that published is published and all other manuscripts do not exist.
In this case, "published" is generally the threshold of receiving the decision letter from the journal Editor that the paper is accepted for publication. In this case the manuscript may be listed as "in press". Yes, this is a holdover term from the old days. Some people, and institutions requiring you to submit a CV, insist that this is the minimum threshold.
But there are other situations in which there are no rules and you can get away with whatever you like.
I'd suggest two rules of thumb. Try to follow the community standards for whatever the purpose and avoid looking like a big steaming hosepipe of vapor.
"In preparation" is the slipperiest of terms and is to be generally avoided. I'd say if you are anything beyond the very newest of authors with very few publications then skip this term as much as possible.
I'd suggest that "in submission" and "under review" are fine and it looks really good if that is backed up with the journal's ID number that it assigned to your submission.
Obviously, I suggest this for manuscripts that actually have been submitted somewhere and/or are out for review.
It is a really bad idea to lie. A bad idea to make up endless manuscripts in preparation, unless you have a draft of a manuscript, with figures, that you can show on demand.
Where it gets tricky is what you do after a manuscript comes back from the journal with a decision.
What if it has been rejected? Then it is right back to the in preparation category, right? But on the other hand, whatever perception of it being a real manuscript is conferred by "in submission" is still true. A manuscript good enough that you would submit it for consideration. Right? So personally I wouldn't get to fussed if it is still described as in submission, particularly if you know you are going to send it right back out essentially as-is. If it's been hammered so hard in review that you need to do a lot more work then perhaps you'd better stick it back in the in preparation stack.
What if it comes back from a journal with an invitation to revise and resubmit it? Well, I think it is totally kosher to describe it as under review, even if it is currently on your desk. This is part of the review process, right?
Next we come to a slightly less kosher thing which I see pretty frequently in the context of grant and fellowship review. Occasionally from postdoctoral applicants. It is when the manuscript is listed as "accepted, pending (minor) revision".
Oh, I do not like this Sam I Am.
The paper is not accepted for publication until it is accepted. Period. I am not familiar with any journals which have accepted pending revision as a formal decision category and even if such exist that little word pending makes my eyebrow raise. I'd rather just see "Interim decision: minor revisions" but for some reason I never see this phrasing. Weird. It would be even better to just list it as under review.
Final note is that the acceptability of listing less-than-published stuff on your CV or biosketch or Progress Report varies with your career tenure, in my view. In a fellowship application where the poor postdoc has only one middle author pub from grad school and the two first author works are just being submitted...well I have some sympathy. A senior type with several pages of PubMed results? Hmmmm, what are you trying to pull here. As I said above, maybe if there is a clear reason to have to fluff the record. Maybe it is only the third paper from a 5 yr grant and you really need to know about this to review their continuation proposal. I can see that. I have sympathies. But a list of 8 manuscripts from disparate projects in the lab that are all in preparation? Boooo-gus.