Что означают эти терминальные сигналы?

Здесь есть страница руководства - я думаю, что вы имеете в виду:

Signal     Value    Action       Comment
-------------------------------------------------------------------------
SIGKILL          9       Term    Kill signal
SIGTERM         15       Term    Termination signal

Вот некоторые другие сигналы:

• Ctrl + C при работающем процессе в терминале отправляет сигнал прерывания клавиатуры:
  SIGINT 2 Term Interrupt from keyboard , Это не всегда останавливает программу прямо, часто она просто завершает ту часть своей работы и затем останавливается.

• Ctrl + \ о работающем процессе в терминале отправляет сигнал выхода:
  SIGQUIT 3 Core Quit from keyboard

• Сигнал по умолчанию, посылаемый killall PROCESS-NAME:
  SIGTERM 15 Term Termination signal. Это также значение по умолчанию, отправляемое из top при нажатии k и входе в процесс PID

Чтобы убедиться, что процесс остановлено, вы можете использовать SIGKILL (или, альтернативно, SIGSTOP), поскольку это не может быть перехвачено, заблокировано или проигнорировано программой.

Вот более длинный список по вышеуказанной ссылке, для справки:

   Signal     Value     Action   Comment
   -------------------------------------------------------------------------
   SIGHUP        1       Term    Hangup detected on controlling terminal
                 or death of controlling process
   SIGINT        2       Term    Interrupt from keyboard
   SIGQUIT       3       Core    Quit from keyboard
   SIGILL        4       Core    Illegal Instruction
   SIGABRT       6       Core    Abort signal from abort(3)
   SIGFPE        8       Core    Floating point exception
   SIGKILL       9       Term    Kill signal
   SIGSEGV      11       Core    Invalid memory reference
   SIGPIPE      13       Term    Broken pipe: write to pipe with no readers
   SIGALRM      14       Term    Timer signal from alarm(2)
   SIGTERM      15       Term    Termination signal
   SIGUSR1   30,10,16    Term    User-defined signal 1
   SIGUSR2   31,12,17    Term    User-defined signal 2
   SIGCHLD   20,17,18    Ign     Child stopped or terminated
   SIGCONT   19,18,25    Cont    Continue if stopped
   SIGSTOP   17,19,23    Stop    Stop process
   SIGTSTP   18,20,24    Stop    Stop typed at tty
   SIGTTIN   21,21,26    Stop    tty input for background process
   SIGTTOU   22,22,27    Stop    tty output for background process

   The  signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.

   Next the signals not in the  POSIX.1-1990  standard  but  described  in
   SUSv2 and POSIX.1-2001.

   Signal       Value     Action   Comment
   -------------------------------------------------------------------------
   SIGBUS      10,7,10     Core    Bus error (bad memory access)
   SIGPOLL             Term    Pollable event (Sys V). Synonym of SIGIO
   SIGPROF     27,27,29    Term    Profiling timer expired
   SIGSYS      12,-,12     Core    Bad argument to routine (SVr4)
   SIGTRAP        5        Core    Trace/breakpoint trap
   SIGURG      16,23,21    Ign     Urgent condition on socket (4.2BSD)
   SIGVTALRM   26,26,28    Term    Virtual alarm clock (4.2BSD)
   SIGXCPU     24,24,30    Core    CPU time limit exceeded (4.2BSD)
   SIGXFSZ     25,25,31    Core    File size limit exceeded (4.2BSD)

   Up  to and including Linux 2.2, the default behaviour for SIGSYS, SIGX-
   CPU, SIGXFSZ, and (on architectures other than SPARC and  MIPS)  SIGBUS
   was  to  terminate  the  process (without a core dump).  (On some other
   Unices the default action for SIGXCPU and SIGXFSZ is to  terminate  the
   process  without  a core dump.)  Linux 2.4 conforms to the POSIX.1-2001
   requirements for these signals, terminating the  process  with  a  core
   dump.

   Next various other signals.

   Signal       Value     Action   Comment
   --------------------------------------------------------------------
   SIGIOT         6        Core    IOT trap. A synonym for SIGABRT
   SIGEMT       7,-,7      Term

   SIGSTKFLT    -,16,-     Term    Stack fault on coprocessor (unused)
   SIGIO       23,29,22    Term    I/O now possible (4.2BSD)
   SIGCLD       -,-,18     Ign     A synonym for SIGCHLD
   SIGPWR      29,30,19    Term    Power failure (System V)
   SIGINFO      29,-,-         A synonym for SIGPWR
   SIGLOST      -,-,-      Term    File lock lost
   SIGWINCH    28,28,20    Ign     Window resize signal (4.3BSD, Sun)
   SIGUNUSED    -,31,-     Term    Unused signal (will be SIGSYS)

   (Signal 29 is SIGINFO / SIGPWR on an alpha but SIGLOST on a sparc.)

   SIGEMT  is  not  specified in POSIX.1-2001, but nevertheless appears on
   most other Unices, where its default action is typically  to  terminate
   the process with a core dump.

   SIGPWR (which is not specified in POSIX.1-2001) is typically ignored by
   default on those other Unices where it appears.

   SIGIO (which is not specified in POSIX.1-2001) is ignored by default on
   several other Unices.