Ulrich's Periodicals Directory (often referred to as UlrichsWeb) is a database that the University Library subscribes to. You may be told to "check Ulrich's," but what does that mean?
Ulrich's will tell you if a journal is still in print, available online, where it is indexed, and most critically, what type of journal it is (scholarly, trade, popular, etc.). This is useful not only for students being asked to find specific types of sources, but also for faculty considering where to publish regardless of where they are in the RTP process.
Ulrich's does not tell you if a journal is good or bad. It just gives you classifications and you make the final judgment.
This is a trade title (as opposed to scholarly or popular). Several departments on campus support publishing in trade journals, but just like with a scholarly title, you should consult with personnel procedures to make sure which ones are considered the strongest for your file. For example, a department might require 3 peer-reviewed articles, and then encourage 1-3 trade journals. Finally, if you publish in a trade journal, it should be relevant to your trade. For example, American Libraries is written by and for librarians and information professionals and is not interchangeable with Hollywood Reporter. When there is a promotion on the line, it pays to consider everything very carefully.
Sample search (scholarly)
Say you did a search for the Journal of Popular Culture:
You can see that this is an actively published title by Wiley-Blackwell, and the jersey icon indicates that it is refereed/peer-reviewed. There are links to take you to the journal's homepage, where you can find information about submission (and potentially acceptance rates), members of the editorial board, and any calls for special issues. Based on this content, you could be reasonably confident that an article published in this journal would "count" for the RTP review as it is a reputable/scholarly title. A caveat: your department might have preferred lists of journals that are "best" to publish in, so you should always make sure you are meeting those suggestions, especially if they are described in personnel procedures.