A root cause is an underlying reason that meaningfully explains an observed failure and guides prevention or correction. It is different from the first visible symptom or a convenient guess. Establishing it can require comparisons, logs and operational evidence, especially when several independent systems contribute to a viewing setup or account workflow at the same time.
A practical example
A player repeatedly buffering is a symptom. Evidence may later show that a failing local cable caused an unstable link; replacing the cable and confirming the link's behaviour supports a more specific explanation than simply labelling the service unreliable.
A common misunderstanding
Do not claim a root cause solely because a restart temporarily changed the symptom. A workaround can restore use without proving which underlying condition triggered the original problem.
Related terms
General operational definition; actual service terms remain separate. Editorial approach