A RCDLCK basically when the system locks 1 record in a file from use. A user may have a record displayed for update on their screen. When the exit the screen it will release the record lock.
An OBJLCK is when the system locks an entire file (or other object) from use by other jobs. This is frequently done with files when performing backups to prevent failures.. It may also happen when a program tries to get data from a data area, like the next sequential order#, Lock the data area, retrieve the data, update with the new number then release the lock.