vmkcore,memory dump,zdump

Vmkcore (vmkcore)
The core dump partition where the Vmkernal puts memory dump information in the event of a "purple screen of death" or a "kernel panic"

Hostd :

This is the process or daemon for vi connectivity  to the ESX server.

core dump partition:

This is the partition created while installing ESX, this partition is used to dump the core's created when the machine PSOD's.

esxcfg-dumppart -l , this command will give you the information of core dump partition.

PSOD:

Purple screen of Death, if any exceptions or asserts are created by any process or memory handlers for MCE (memory check exception) this PSOD is gnenerated, this will bring machine to halt. you have to reboot to bring mahcine to normal state.

Zdump:

this is the core dump file created when machine generates an exception or assert (PSOD).

vmkdump  --zdumpname < zdump file >, this command will unzip the core dump generated into human readable file.