A direct path read I/O operation reads data into the session's PGA instead of the SGA. Direct read I/Os may be performed in synchronous or asynchronous mode, depending on the platform and the value of the DISK_ASYNC_IO parameter. An Oracle session waits for a direct read I/O request to complete on the direct path read wait event. Direct I/O is normally used when reading from sort segments. Parallel query slaves also use direct I/O when scanning a table or index. As of Oracle 8.1.7, there is a separate direct read I/O wait event for LOB segments - direct path read (lob).
This is a companion discussion topic for the original entry at https://blog.toadworld.com/wait_events_-_direct_path_read