The name of the kernel variable in Solaris which stores the PID of the most recently executed process. Each time a new process is executed, it is assigned the first available PID "after" (in the cyclic sense--PIDs wrap around at about 30000) the value in mpid. Here's an example of how to read the value of mpid:

# adb -k /dev/ksyms /dev/mem
physmem de02
mpid:           6093

You can also write to this variable using adb, which is sometimes fun but rarely useful. On some versions of Solaris, weird things happen if you set it above 30000, however later versions just wrap around sensibly to the first available PID after 0 when you do this. (It seems that earlier kernels check for the wraparound condition with "if (mpid == PID_MAX)" whereas these days they do "if (mpid >= PID_MAX)".)