  In order to study two-sided skew braces, we introduce the notion of weakly
trivial skew braces. We give a classification of such skew braces and show that
they are essential in the study of two-sided skew braces. As an application, we
obtain new and generalize known results relating the additive and
multiplicative group of two-sided skew braces. Further, we show that two a
priori different notions of prime and semi-prime skew braces, as introduced by
Konovalov, Smoktunowicz and Vendramin, coincide for two-sided skew braces.
