Downmarket Goes Mainstream
Clayton Christensen defined this in 1995 as the process where:
A smaller company challenges an incumbent by serving needs at the bottom of the market (a segment often ignored by the incumbent) at a reduced cost.
As the incumbent continues to ignore these developments, the smaller company eventually moves upmarket and offers solutions “good enough” for the incumbent’s mainstream consumers.
Disruption happens once the incumbent’s mainstream consumers are attracted by the small company’s offer.