we are talking about legal term.
Still not legally incest. Most states have different laws as to what defines incest anyway, most states it is legal to marry your first cousin, new jersey and rhode island incest is legal as long as both people are 18 but its illegal for them to marry, the term itself is subjective, but step siblings or step parents would not be incest since the term itself and the laws were put in place to keep relatives from breeding which introduces the possibilty for recessive genes to occur in the children and the chances become exponentially greater if children born to incest were then to breed with eachother, google "habsburg chin" if you'd like to see a minor example, or google all the medical issues king tut had for a major example, his parents were brother and sister and he was supposed to marry his own sister but it wasnt possible so he married his grandmother instead, thats a big part of the reason royals in europe used to marry their daughters off to other countries, partly for alliances but also to try and keep the genepool from getting pee'd in, all european royals were related but not direct relations, except for the occasional first cousins marrying, even today the remaining monarchies in europe are still all related, the british royal family are members of the saxe-coburg-gotha family, the name windsor was one they adopted from windsor castle in 1917 after WW1 when a german surname would be seen as a little problematic in England, the british royal family are in fact german and they were fond of incest as well until a little over a century ago, one royal prince was so weak because of bad genes from inbreeding that his neck muscles were not strong enough to hold his head upright.