This topic applies to the Power Query Formula Language (informally known as "M") which can be used with Power Query and Power BI Desktop to build queries that mashup data. See the list of function categories.

Expands a column of records or a column of tables into multiple columns in the containing table.

Table.ExpandTableColumn(table as table, column as text, columnNames as list, optional newColumnNames as nullable list) as table  

tableThe Table to modify.
columnThe column to expand.
columnNamesList of column names.
optional newColumnNamesOptional list of new column names.