Depending on the type of tables that are queried for a report, the maximum number of rows in the report can vary.
Most reports query smaller aggregate tables designed specifically for those reports. The row limit under these circumstances is 50K.
There are other implementation-specific circumstances (e.g., when a report queries a table associated with a particular product integration) under which the row limit can exceed 50K. Implementation-specific circumstances are subject to change and so the limit can vary, but will not fall below 50K.
When you change the default query for a report, for example, by adding comparisons or a secondary dimension, the report may then query a larger aggregate table. The row limit under these circumstances is 2M.
When the query for a report returns more rows than the limit, the excess rows are rolled up under (other). Under these circumstances, the dimension information for the excess rows is not displayed -- it is all aggregated as (other) -- but the metric totals for all of the data retrieved are correct. (Learn more about (other) entries.)