There is a type of macro used within the low-level discovery function:
It is a macro that is used in an LLD rule and returns real values of file system names, network interfaces and SNMP OIDs.
These macros can be used for creating item, trigger and graph prototypes. Then, when discovering real file systems, network interfaces etc., these macros are substituted with real values and are the basis for creating real items, triggers and graphs.
These macros are also used in creating host and host group prototypes in virtual machine discovery.
LLD macros can be used:
In all those places LLD macros can be used inside user macro context.
Some low-level discovery macros come "pre-packaged" with the LLD function in Zabbix - {#FSNAME}, {#FSTYPE}, {#IFNAME}, {#SNMPINDEX}, {#SNMPVALUE}. However, adhering to these names is not compulsory when creating a custom low-level discovery rule. Then you may use any other LLD macro name and refer to that name.