What is the meaning of "To appear" for submitted papers

Based upon the context, I would treat to appear as a synonym to accepted or in press. This article means has been accepted, but not yet published. Most journals have a lag between acceptance and online publication (conversely, others journals now post the accepted manuscript almost immediately after acceptance). This lag can be due to a backlog of other articles ahead of yours, copy editing, formatting, or other procedural delays. Before online early access, articles could spend months or longer in this status (e.g., an article was accepted for quarterly publication and had to wait multiple quarters to be published).

Another question asks about how article status is evaluated by search committees. I would also add that you likely have no way of verifying to appear other than waiting. I have heard about search committees and tenure/promotion committees asking for copies of acceptance letters, however.

It probably means more than that - it indicates that the paper has been accepted. If it's just been submitted, there's a nontrivial chance of rejection, so it might not appear; however after a paper's been accepted it's very rare for the paper not to be published, so one can say "to appear".