Tom Collins explains a database wait:
SQL Server Log truncation deletes inactive Virtual Log Files (VLF) from the SQL Server database transaction log . The Log truncation process frees space in the logical log for reuse by the Physical transaction log. If no truncation occurs , eventually it will fill all the disk space allocated to physical log files.
SQL Server Log truncation can be delayed for a range of different reasons.A good starting point is to query the sys.databases log_reuse_wait and log_reuse_wait_desc columns. This will supply different waits describing the reason for a delay
Read on for more info about the OLDEST_PAGE wait.