To be able to use Munin, to understand the documentation, and - not to be neglected - to be able to write documentation that is consistent with Munin behaviour, we need a common nomenclature.

Common terms

Term Explanation Also referred to as as
Munin Master The central host / server where Munin gathers all data. The machine runs munin-cron master, server, munin server
Munin Node The daemon / network service running on each host to be contacted by the In SNMP terms it may be called an agent.
Plugin Each munin node handles one or more plugins to monitor stuff on hosts service
Host A machine monitored by Munin, maybe by proxy on a munin node, or via a SNMP plugin  
Field Each plugin presents data from one or more data sources. Each found, read or calculated value corresponds to a field.attribute tuple. Data source
Attribute Description found in output from plugins, both general (global) to the plugin, and also specific ot each Field.  
Environment variable Set up by munin node, used to control plugin behaviour. Found in the plugin configuration directory. (/etc/munin/plugin-conf.d/)  
Global (plugin) attribute Used in the global context in the configuration output from a plugin. (Note: The attribute is considered “global” only to the plugin (and the node), and only when executed.  
Datasource specific plugin attribute Used in the datasource-specific context in the output of a plugin  
Global directive Used in munin.conf  
Node level directive Used in munin.conf  
Group level directive Used in munin.conf  
Field level directive Used in munin.conf  


To shed some light on the nomenclature, consider the examples below:

Global plugin attribute

Global plugin attributes are in the plugins output when run with the config argument. The full list of these attributes is found on the protocol config page. This output does not configure the plugin, it configures the plugins graph.

graph_title Load average
----------- ------------
     |           `------ value
     `------------------ attribute

Datasource specific plugin attribute

These are found both in the config outout of a plugin and in the normal readings of a plugin. A plugin may provide data from one or more data sources. Each data source needs its own set of field.attribute tuples to define how the data source should be presented.

load.warning 100
---- ------- ---
  |     |     `- value
  |     `------- one of several attributes used in config output
  `------------- field

load.value 54
---- ----- --
  |    |    `- value
  |    `------ only attribute when getting values from a plugin
  `----------- field

Configuration files

This one is from the global section of munin.conf:

dbdir       /var/lib/munin/
-----       ---------------
  |                `--------- value
  `-------------------------- global directive

And then one from the node level section:

  address localhost
  ------- ---------
     |        `----- value
     `-------------- node level directive