From the NannyMUD documentation

LAST CHANGE

2000-12-20

FUNCTION

NAME
        mapping - An associative array.


SYNTAX
	map = ([ index1:data1 , index2:data2 , ... ]);
	data = map[index1];

DESCRIPTION
	OPERATORS
	[], +
	m_delete, mkmapping, mappingp, m_values, m_indices, m_sizeof
	map_mapping, filter_mapping

	A mapping is basically an array that can be indexed on any type, not
	not just integers. It can also be seen as a way of linking data
	(usually strings) together. It consists of a lot of index-data pairs
	which are linked togeter in such a way that map[index1] returns data1.
	It is also possible to set that data by writing map[index1]=new_data1.
	If you try to set an index in a mapping that isn't already present in
	the mapping then it will be added. If you ask for the data of an index
         that does not exist, you will get a zero, 0.