Scholars’ attention to the concept of niche parties has greatly increased. While researchers agree that niche parties matter in a variety of ways, the definitions and measurements of such parties are manifold and an accordance remains yet to be found. I argue the given conceptualizations of niche parties (a) suffer from gaps between their measurements and theoretical concepts or (b) conceptual clarity. The theoretical concept I propose understands niche parties as (a) predominantly competing on niche market segments neglected by their competitors and (b) not discussing a broad range of these segments. By measuring exactly these two components in an additive index drawn from the MARPOR data, the validation shows that parties emphasizing niche segments differentiate themselves from their competitors also by using a condensed message on these segments. In particular, this component of party competition, the specialization of party offers, has not been studied in the literature on niche parties and should receive more attention.