The US dollar is the dominant vehicle currency in FX and commodities invoicing. “USD strength” in research usually means broad trade-weighted or DXY-style baskets, or specific crosses (EURUSD, USDJPY), not a single exchange listing.
Research use: rate differentials, fiscal/issuance narratives, and risk-on/off dollar demand drive regimes. Always specify the cross or index; USD alone is incomplete without a quote pair.