Occam’s razor (also written as Ockham’s razor, and lex parsimoniae in Latin, which means law of parsimony) is a problem-solving principle attributed to William of Ockham (c. 1287–1347), who was an English Franciscan friar, scholastic philosopher and theologian. The principle can be interpreted as stating “Among competing hypotheses, the one with the fewest assumptions should be selected.” [Ed. i.e. choose the simplest explanation]
Hanlon’s razor is an aphorism expressed in various ways including “Never attribute to malice that which is adequately explained by stupidity,” or “Don’t assume bad intentions over neglect and misunderstanding.” It recommends a way of eliminating unlikely explanations for a phenomenon (a philosophical razor).
Heinlein’s razor: variant of Hanlon’s razor. Never attribute to malice that which can be adequately explained by stupidity, but don’t rule out malice. [Ed. Heinlein was a rather skeptical fellow.]
Relate’s razor: variant of Hanlon’s razor. “In a relationship, never attribute to malice what can adequately be explained by the other party being ignorant or oblivious. Ask questions to determine intent and don’t jump to conclusions.”