how to check if NLS patch already applied on each APPL_TOP

Hi
Base on Note 364439.1 Tips and Queries for Troubleshooting Advanced Topologies
In 2-node environment (Non-shared APPL_TOP)
To check if a certain patch was applied on each APPL_TOP
the method (use the AD_BUGS table to see if patches are applied) isn't accurate
we need to use the method mentioned on section "Checking the Patch Requirements on each Appl_Top"

After run the command on that section, we can got the result like following

dcollierbe:
..Patch 8919491 was EXPLICIT
..Patch 9239090  was EXPLICIT
.
dcollieremt:
..Patch 8919491 was NOT_APPLIED
..Patch 9239090  was NOT_APPLIED

1.Could you tell me What does EXPLICIT meant to me here