Q: What does the status "Pending'' mean?

Since you haven't mentioned whether any other statuses were displayed before this, I assume this is the first status change you have seen after submission. If that is the case, there is a possibility that your submission has not been completed. Generally, once the submission is successfully completed, the status shows "Submitted successfully" or "Submission complete."  

If you have not come across these statuses, there must be something pending in your submission package that you have not noticed. Please go back to the submissions page and check if you have filled all the fields in the form and uploaded all the required documents.

Alternatively, if the status showed "Submissions completed" and then changed to "Pending," it could mean that the editorial assistants have not yet looked at your paper. This means that the admin check of your paper is still pending and once it is done, it will be assigned to an Associate Editor.

Related reading:

• Can you help me understand the current status of my manuscript on the online submission system?
• Why does the status change from "Editor Assigned" to "Editor Invited" and back to "Editor Assigned"?
• Why is my paper not assigned to an editor even a month after submission?