An unclear, void, borderline or inconclusive result means it's not possible to give a result from the test taken this time. This can be for several different reasons.
If this happens, you may be advised to ask for another coronavirus test. Do this as soon as possible, as the test is most accurate within a few days of your symptoms starting.
If you're not able to have another test, you and anyone you live with must self-isolate at home in line with the UK Government self-isolation guidance: https://www.gov.uk/government/publications/covid-19-stay-at-home-guidance.