Q has made reference to D5 in multiple posts. It likely has more than one meaning. It’s been posted at times where it’s clear that it was referring to a date (i.e. December 5). But other posts seem to be referring to something else. One likely suggestion is that it refers to an the classification of avalanches (D1-D5, with D5 being the most extreme and destructive avalanche). You can go to Qanon.pub and do a search for it. It’s in about 24 posts.
Q ‘language’ is often misleading or confusing.