The term, mansplaining, came into popular usage after Rebecca Solnit wrote the essay on a man explaining to her the significance of the book that she herself had written:
Here's an excerpt from this essay:
"Men explain things to me, and to other women, whether or not they know what they're talking about. Some men. Every woman knows what I mean. It's the presumption that makes it hard, at times, for any woman in any field; that keeps women from speaking up and from being heard when they dare; that crushes young women into silence by indicating, the way harassment on the street does, that this is not their world. It trains us in self-doubt and self-limitation just as it exercises men's unsupported overconfidence." - Rebecca Solnit
HERstory: In feminist use, history emphasizing the role of women or told from a woman's point of view; also, a piece of historical writing by or about women. (from the Oxford English Dictionary)
Herstory is one of those thorny words in feminist theory, that invites a great deal of controversy. Some people view it, at worst, as unnecessarily inflammatory. At best, it is seen as overly politically correct.
Whether or not you object to the term itself, you may agree that it is important to reflect on historical events from a woman's perspective.
History tends to be written by the conquerors, and those conquerors, for the most part, have been men. Specifically white men. This phenomenon explains why women feel that their experience is not accurately reflected in most history books.