A supernatural gift, a revelation, which enables us to see the source or root of the problem. This is not a natural discernment (working things out), but a spiritual impression that we can name e.g. spirit of infirmity, divination. We can discern the activity of the Holy Spirit, demonic activity, or angelic activity. We don't sit as judge, but look as an observer, and ask God how we should deal with it.
Words of Knowledge; Prophecy; and Discerning of Spirits all need to be accompanied with a Word of Wisdom - know what to do with what we receive.