You inquire how to interpret the distinct values (IDR, NIDR, NULL) for the column MeterTypeCode in the Load Profile table in Aurea.
As per the Load Profiling Guide (ERCOT), the terms IDR and NIDR stand for Interval Data Recorder and Non-Interval Data Recorder, respectively. A value NULL for the column MeterTypeCode in the Load Profile table indicates that there is no value updated for that record.
For your reference, the following query can be run on the replication database in your environment to get the values for the column MeterTypeCode from the Load Profile table.
select distinct Metertypecode from loadprofile