What is acpitz-virtual?

lm-sensors gives the following output for this machine:

acpitz-virtual-0
Adapter: Virtual device
temp1:       +60.0°C  (crit = +105.0°C)                  
temp2:       +56.0°C  (crit = +105.0°C)                  
temp3:       +35.3°C  (crit = +105.0°C)                  
temp4:       +75.0°C  (crit = +110.0°C)                  
temp5:       +65.0°C  (crit = +256.0°C)                  
temp6:       +63.0°C  (crit = +105.0°C)                  

coretemp-isa-0000
Adapter: ISA adapter
Core 0:      +66.0°C  (high = +100.0°C, crit = +100.0°C)  

coretemp-isa-0001
Adapter: ISA adapter
Core 1:      +66.0°C  (high = +100.0°C, crit = +100.0°C) 

I would like to know what the acpitz-virtual sensor is. It seems to be some sort of replication of acpi thermal zones but /proc/acpi only contains

ac_adapter
battery
button
event
wakeup

so there don't seem to be any temperature sensors. Can somebody make sense of this?

What does the acpitz-virtual sensor output refer to?

The acpitz refers to the 'ACPI thermal zone'. There was some discussion about renaming the thermal zones on the lm-sensors mailing list:

We could probably update the code so that the labels default to the ACPI thermal zone names. Sometimes these names are useful... but sometimes not.

From the same reply above, there is a way too look up the ACPI table (with a caveat):

Look in /sys/class/thermal/thermal_zone*/device/path. The last item of the path is the device name. But as said above, these are 4-digit names for ACPI internal use, usually not meaningful enough for humans.

Other acpitz-virtual outputs can refer to the CPU socket temperature (see also Thermal sensors on the ThinkWiki or the base of the CPU, as per this Ubuntu forums post:

"acpitz-virtual-0" is probably a sensor diode either in the CPU socket, or nearby on the motherboard.