How many column types does Druid's have

I know there is dimension column, metric column, and timestamp column. For example if I have column A, B, C, and I specify column A and B as dimension, then I think C will not be dimension. My question is what is the column type of C? or can I query column C at all?

If you define column A and B in your ingestion spec but not C, and C appears in some rows, C will be added as a String-typed column for that datasource.

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