The columns of the scheduler/agents tables aren't all documented. I remember there was one or two documents in MOS explaining the meaning of a column or two, but that's it.

It isn't a table meant for direct access and usage. That table, like the others, is used by the tool and by Job Manager.

You could deduct the meaning by looking at few entries with different values and check what Job Managers tells you about them, and trying to confirm your deducted meaning by testing with some agents etc.