what does a STAT of I mean for ps -aux? "I" does not appear on the man page

Question

ps -aux | grep "I<"
root         4  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/0:0H]
root         6  0.0  0.0      0     0 ?        I<   16:15   0:00 [mm_percpu_wq]
root        18  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/1:0H]
root        24  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/2:0H]
root        30  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/3:0H]
root        32  0.0  0.0      0     0 ?        I<   16:15   0:00 [netns]
root        40  0.0  0.0      0     0 ?        I<   16:15   0:00 [writeback]
root        44  0.0  0.0      0     0 ?        I<   16:15   0:00 [crypto]
root        45  0.0  0.0      0     0 ?        I<   16:15   0:00 [kintegrityd]
root        46  0.0  0.0      0     0 ?        I<   16:15   0:00 [kblockd]
root        47  0.0  0.0      0     0 ?        I<   16:15   0:00 [ata_sff]
root        48  0.0  0.0      0     0 ?        I<   16:15   0:00 [md]
root        49  0.0  0.0      0     0 ?        I<   16:15   0:00 [edac-poller]
root        50  0.0  0.0      0     0 ?        I<   16:15   0:00 [devfreq_wq]
root        51  0.0  0.0      0     0 ?        I<   16:15   0:00 [watchdogd]
root        56  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/u9:0]
root        99  0.0  0.0      0     0 ?        I<   16:15   0:00 [kthrotld]
root       100  0.0  0.0      0     0 ?        I<   16:15   0:00 [acpi_thermal_pm]
root       102  0.0  0.0      0     0 ?        I<   16:15   0:00 [ipv6_addrconf]
root       111  0.0  0.0      0     0 ?        I<   16:15   0:00 [kstrp]
root       129  0.0  0.0      0     0 ?        I<   16:15   0:00 [charger_manager]
root       177  0.0  0.0      0     0 ?        I<   16:15   0:00 [scsi_tmf_0]
root       179  0.0  0.0      0     0 ?        I<   16:15   0:00 [scsi_tmf_1]
root       181  0.0  0.0      0     0 ?        I<   16:15   0:00 [scsi_tmf_2]
root       183  0.0  0.0      0     0 ?        I<   16:15   0:00 [scsi_tmf_3]
root       185  0.0  0.0      0     0 ?        I<   16:15   0:00 [scsi_tmf_4]
root       187  0.0  0.0      0     0 ?        I<   16:15   0:00 [scsi_tmf_5]
root       193  0.0  0.0      0     0 ?        I<   16:15   0:00 [e1000e]
root       202  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/3:1H]
root       205  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/0:1H]
root       229  0.0  0.0      0     0 ?        I<   16:15   0:00 [ext4-rsv-conver]
root       273  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/2:1H]
root       285  0.0  0.0      0     0 ?        I<   16:15   0:00 [kworker/1:1H]

Answer 1

It does appear in the man page:

PROCESS STATE CODES
       Here are the different values that the s, stat and state output specifiers
       (header "STAT" or "S") will display to describe the state of a process:

           D    uninterruptible sleep (usually IO)
           I    Idle kernel thread
           R    running or runnable (on run queue)
           S    interruptible sleep (waiting for an event to complete)
           T    stopped by job control signal
           t    stopped by debugger during the tracing
           W    paging (not valid since the 2.6.xx kernel)
           X    dead (should never be seen)
           Z    defunct ("zombie") process, terminated but not reaped by its parent

       For BSD formats and when the stat keyword is used, additional characters
       may be displayed:

           <    high-priority (not nice to other users)
           N    low-priority (nice to other users)
           L    has pages locked into memory (for real-time and custom IO)
           s    is a session leader
           l    is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
           +    is in the foreground process group