Yes, the real pending balance, which is the balance which is not matured yet. What is now labeled as "pending balance" is in fact the pending payment, i.e. the matured balance which isn't paid out yet.

Pending balance --> Matured balance (or just balance) --> Paid balance

This is the logical sequence of events.

Indeed sometimes part of a pending balance does not mature when a block gets orphaned. This is not a problem and it happens very rarely.

Most confusion and questions (like the one a few posts above) on these threads arise from the problem described above, from the not shown pending balance. Other types of pools like MPOS do show the pending=unmatured balance immediately after a block was found. They however do check right away if a block was orphaned. The cryptonote pool checks only when each particular block is supposed to mature, in this case 20 blocks later. Anyway, orphaned blocks are no problem at all as the pending balance simply would get updated or by not having their rewards mature once they are identified (no matter when).