Depending on the particulars of how the journal operates and how much of the review process it makes visible, this is likely to mean one of two things with respect to the standard journal workflow:
- Most likely, the journal simply reports "under review" for all manuscript that have not yet received a decision. In this case, it probably means that your manuscript is still undergoing initial processing and hasn't yet been assigned to a handling editor.
- If the journal gives finer-grained status information about the workflow (e.g., "assigning reviewers", "under review", "waiting for decision"), then it would likely mean that the paper is with reviewers, but that something has happened to require a change of handling editors, which is now ongoing.
The first is much more likely than the second, particularly if the paper is recently submitted.