Powerscaling refers to a method of inductive reasoning used to determine the strength of various fictional characters/entities. This method can assign levels of power to a character who has demonstrated few, or even no actual Feats. Powerscaling is based on heirarchical logic, narrative statements, and word - of - mouth. As such, it may, be wrong and unreliable.
An example of Powerscaling: Whitebeard is stated to be the strongest living character in One Piece. We've only seen him fight once, and even then it was just one attack, with an atmospheric affect. However, powerscaling can be used to estimate his true power by comparing it to the power of other characters we have seen. For example, we know he must be stronger than Ace (since he commands Ace), as well as Admirals Aokiji and Kizaru, Rayleigh, Garp, Moria, Kuma, Mihawk, and all of the other top tiers in One Piece who we have seen fight. This can further be extrapolated to say he has some means of dealing with their devil fruits, and can likely create larger and more powerful explosions/attacks than them, and is also likely faster.
*The preceding paragraph was written before Whitebeard showed his abilities in the manga, and the prediction from powerscaling turned out to be basically true
Powerscaling is often used for the Dragon Ball series to give out a higher given precedent of strength from far weaker fighters in the series.
As you can see, powerscaling usually falls into the realm of speculation. While it can sometimes give you a general idea of the power of a character, it is not always reliable as concrete evidence in a debate.