Pending merge means that you or someone else merged two profiles together (either to create a cycle or to eliminate duplicate siblings / spouses / etc.) The point of a "pending" merge is that it can be undone. While the merge is pending, you will see a primary profile in every place where either of those two profiles previously appeared, and from the profile page of the primary profile, you can access the "secondary" profile -- the one that will be eliminated once the merge is complete.
Once you're certain the two merged profiles are actually the same person, you should complete the merge (Complete Merge button atop the profile page of the secondary profile) and then delete the secondary profile once you've verified that the primary profile contains all of the data that was previously in the secondary profile. We'll be working to streamline this process in a future release.