Introduced in December 2020, the DEFINE COLUMN statement lets you define a calculated column local to a query. The column is not persisted in the model, it exists only for the lifetime of the query. Apart from that, it is a calculated column in every sense of the term.
The extension of DAX with the capability to define calculated columns local to a query is needed in order to support composite models over Analysis Services (AS). There are no limitations in the use of the feature. For this reason, you can take advantage of local columns in any DAX query. We refer to calculated columns defined in a query as query calculated columns, or query columns for short.
Click through to see it in action. I like this idea a lot, though do read their note regarding performance, contrasting it with ADDCOLUMNS.