When you say "relative majority", do you mean a plurality (50% or less, so not a majority, but more than any other party), or is this situation more complicated than it seems?
It's a plurality. "Relative majority" is a direct translation from the Portuguese expression "maioria relativa" .
Curiously, I actually searched for the term rather than directly translate. Seems it's (at least somewhat) used in the UK, even if not in the US.
The right wing party (actually a coalition of 2 right wing "mainstream" parties) was the most voted party but fell way short of a majority (they control 102 seats out of 230) and failed to get parliamentary support.