A single keyword adgroup or SKAG for short is a recommendation we make to ensure a HYPER targeted adgroup with max control over the bid/strategy/budget and corresponding ad(s).
In a standard adgroup you might have multiple, similarly themed keywords that have similar performance and relate to a similar, relevant ad.
However, in some cases, you might want really specific control over a particular keyword or variation. For example, if one keyword has a much higher search volume than others, it can make sense to separate it to control the performance.
Similarly, by splitting this keyword out you can write an even more specific ad, improving CTR and Quality Score.
In CampaignHero - we analyse the performance of your adgroups and the keywords within and recommend splitting out a keyword or keywords when we think that it would have a positive impact on your campaign performance.