Heteroflexible, or Elasexual, is a label describing an individual who is generally straight/heterosexual/heteroromantic and so primarily experiences attraction to the "opposite" or dissimilar gender[s], but is occasionally attracted to the same or similar gender[s].
When a heteroflexible individual does experience attraction to the same gender, the attraction may have more to do with the target of attraction themselves rather than the target's gender. This experience is common for heterosexual individuals in a relationship with a partner who has come out as the same gender (transgender) as them and whom they still want to be together with.
The Kinsey Scale is a way to determine one's sexual preferences through a test. Once one takes the test, they will be given a score from 0-6; 0 being exclusively heterosexual, 6 being exclusively homosexual. Heteroflexible individuals will usually fall at about a 1 on this scale.