A term describing a majority that is bigger than 85% or 90%?
One suitable and often-used phrase is landslide majority.
- An overwhelming majority of votes for one party in an election.
‘winning the election by a landslide’
[as modifier] ‘a landslide victory’Oxford
Of course, overwhelming and its synonyms (as used by Oxford) will also be relevant.
The term super-majority is also heard, but that's different: that is the requirement for a greater majority than merely 50%+1 — for example, requiring a two-thirds majority or some even larger proportion.