"Market maker" refers to a "role" in a market. HFT is simply one way that role is fulfilled, in some markets (equities, futures, ...) but perhaps not others (c

"Market maker" refers to a "role" in a market. HFT is simply one way that role is fulfilled, in some markets (equities, futures, ...) but perhaps not others (corporate bonds, MBS, ...). No market needs HFTs to provide the service, but they exist because in those markets they provide a monumentally better (cheaper) service than their predecessors.