A set is an ordered collection of one or more tuples that have the same dimensionality (see Rules for Specifying Sets for an explanation of dimensionality).
A tuple is a way to refer to a member or a member combination from any number of dimensions. For example, in the Sample.Basic database, Jan is a tuple, as is (Jan, Sales), as is ([Jan],[Sales],[Cola],[Utah],[Actual]).
The member name can be specified in these ways:
By specifying the actual name or the alias; for example:
Cola
Actual
COGS
[100]
If the member name starts with number or contains spaces, it should be within brackets; for example, [100]. Brackets are recommended for all member names, for clarity and code readability.
If the member name starts with an ampersand (&) , it should be within quotation marks; for example, ["&xyz"]. This is because the leading ampersand is reserved for substitution variables (see Using Substitution Variables in MDX Queries). You can also specify it as StrToMbr("&100").
For attribute members, the long name (qualified to uniquely identify the member) should be used; for example, [Ounces_12] instead of [12].
By specifying dimension name or any one of the ancestor member names as a prefix to the member name; for example, [Product].[100-10] and [Diet].[100-10]. This practice is recommended for all member names, as it eliminates ambiguity and enables you to refer accurately to shared members.
By specifying the name of a calculated member defined in the WITH section.