Process status of S+ S S< Sl

Upon checking the process status, I read many strange status

D
I
I<
R+
Rl
S
S+
S<
Sl
Sl+
SLl
SLl+
SN
SNsl
S<s
Ss
Ss+
S<sl
Ssl
Ssl+
STAT
Tl

I learned I (idle,) R(running) , Sleep, but have no ideas the combinations of S+ S<,

What do they mean? What kind of material should be consult with ?

When in doubt, check the manpage. From the command man ps:

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)
               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

Hope this helps!