To be betamaxed is to have your superior product lose out in the market to an inferior one as a result of marketing, influence or some other factor unrelated to product quality.
The term derives from the videotape format wars between Sony's Betamax and JVC's VHS in the 1970s and 1980s. The products were not compatible, so they required different types of VCRs (video cassette recorders). VHS eventually cornered the domestic market, despite being generally considered inferior to Betamax.
The term is also used outside of the realm of technology to describe, for example, a political win by a party you consider inferior.