What do VIRT, RES and SHR mean in the top command?

It can be seen from man top in terminal as

DESCRIPTIONS of Fields Listed below are top's available fields. They are always associated with the letter shown, regardless of the position you may have established for them with the 'o' (Order fields) interactive command.

    Any field is selectable as the sort field, and you control whether
   they  are  sorted  high-to-low  or  low-to-high.   For  additional
   information on sort provisions see topic 3c. TASK Area Commands.

   a: PID  --  Process Id
      The  task's unique process ID, which periodically wraps, though
      never restarting at zero.

   b: PPID  --  Parent Process Pid
      The process ID of a task's parent.

   c: RUSER  --  Real User Name
      The real user name of the task's owner.

   d: UID  --  User Id
      The effective user ID of the task's owner.

   e: USER  --  User Name
      The effective user name of the task's owner.

   f: GROUP  --  Group Name
      The effective group name of the task's owner.

   g: TTY  --  Controlling Tty
      The name of the controlling  terminal.   This  is  usually  the
      device  (serial  port,  pty,  etc.)  from which the process was
      started, and which it uses for input  or  output.   However,  a
      task  need  not  be  associated  with a terminal, in which case
      you'll see '?' displayed.

   h: PR  --  Priority
      The priority of the task.

   i: NI  --  Nice value
      The nice value of the task.  A negative nice value means higher
      priority,  whereas  a positive nice value means lower priority.
      Zero in this field simply means priority will not  be  adjusted
      in determining a task's dispatchability.

   j: P  --  Last used CPU (SMP)
      A  number  representing the last used processor.  In a true SMP
      environment this will likely change frequently since the kernel
      intentionally  uses  weak  affinity.   Also,  the  very  act of
      running top  may  break  this  weak  affinity  and  cause  more
      processes  to  change  CPUs  more  often  (because of the extra
      demand for cpu time).

   k: %CPU  --  CPU usage
      The task's share of the elapsed CPU time since the last  screen
      update, expressed as a percentage of total CPU time.  In a true
      SMP environment, if 'Irix mode' is Off,  top  will  operate  in
      'Solaris  mode' where a task's cpu usage will be divided by the
      total number of CPUs.  You toggle 'Irix/Solaris' modes with the
      'I' interactive command.

   l: TIME  --  CPU Time
      Total  CPU  time  the  task  has  used  since it started.  When
      'Cumulative mode' is On, each process is listed  with  the  cpu
      time  that  it  and  its  dead  children  has used.  You toggle
      'Cumulative mode' with 'S', which is a command-line option  and
      an  interactive  command.   See the 'S' interactive command for
      additional information regarding this mode.

   m: TIME+  --  CPU Time, hundredths
      The same as 'TIME', but  reflecting  more  granularity  through
      hundredths of a second.

   n: %MEM  --  Memory usage (RES)
      A task's currently used share of available physical memory.

   o: VIRT  --  Virtual Image (kb)
      The  total  amount  of  virtual  memory  used  by the task.  It
      includes all code, data and shared libraries  plus  pages  that
      have  been  swapped out and pages that have been mapped but not
      used.

   p: SWAP  --  Swapped size (kb)
      Memory that is not resident but is present in a task.  This  is
      memory  that  has been swapped out but could include additional
      non-resident memory.  This column is calculated by  subtracting
      physical memory from virtual memory.

   q: RES  --  Resident size (kb)
      The non-swapped physical memory a task has used.

   r: CODE  --  Code size (kb)
      The  amount  of virtual memory devoted to executable code, also
      known as the 'text resident set' size or TRS.

   s: DATA  --  Data+Stack size (kb)
      The amount of virtual memory devoted to other  than  executable
      code, also known as the 'data resident set' size or DRS.

   t: SHR  --  Shared Mem size (kb)
      The amount of shared memory used by a task.  It simply reflects
      memory that could be potentially shared with other processes.

   u: nFLT  --  Page Fault count
      The number of major page faults that have occurred for a  task.
      A  page  fault  occurs  when a process attempts to read from or
      write to a virtual page that is not currently  present  in  its
      address  space.   A  major  page  fault is when backing storage
      access (such as  a  disk)  is  involved  in  making  that  page
      available.

   v: nDRT  --  Dirty Pages count
      The  number  of  pages  that have been modified since they were
      last written to disk.  Dirty pages  must  be  written  to  disk
      before  the  corresponding physical memory location can be used
      for some other virtual page.

   w: S  --  Process Status
      The status of the task which can be one of:
         'D' = uninterruptible sleep
         'R' = running
         'S' = sleeping
         'T' = traced or stopped
         'Z' = zombie

      Tasks shown as running should be more properly  thought  of  as
      'ready  to run'  --  their task_struct is simply represented on
      the Linux run-queue.  Even without a true SMP machine, you  may
      see  numerous  tasks  in  this  state  depending on top's delay
      interval and nice value.

For CPU

2c. CPU States The CPU states are shown in the Summary Area. They are always shown as a percentage and are for the time between now and the last refresh.

    us  --  User CPU time
      The time the CPU has spent running users'  processes  that  are
      not niced.

    sy  --  System CPU time
      The  time  the  CPU  has  spent  running  the  kernel  and  its
      processes.

    ni  --  Nice CPU time
      The time the CPU has spent running users'  proccess  that  have
      been niced.

    wa  --  iowait
      Amount of time the CPU has been waiting for I/O to complete.

    hi  --  Hardware IRQ
      The  amount  of  time  the  CPU  has  been  servicing  hardware
      interrupts.

    si  --  Software Interrupts
      The  amount  of  time  the  CPU  has  been  servicing  software
      interrupts.

    st  --  Steal Time
      The  amount  of  CPU  'stolen' from this virtual machine by the
      hypervisor for other tasks (such  as  running  another  virtual
      machine)