Essentially when a man assumes a woman (sometimes a man) lacks knowledge in an area where she (or he) is known to be an expert
Me reading the other definitions of "mansplain": Wow, these all sound like they were written by men who have never experienced mansplaining themselves! Now, they're trying to explain what it is. CLASSIC mansplaining!!

2nd-year law student: I cannot believe Matt just mansplained me about the difference between prosecutors and defense attornies. This dude is referencing TV shows LMAO
by shhhhhhhlj January 27, 2018
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Quite regularly, during team meetings in front of every else, when a woman who is reporting on her own project work with which she is most experienced with and has worked in the field for over twenty years, another peer always feels the need to "complete" her sentences mid-way, talks over her, hijacks her time to shine, taking over the explanations, progress report, issue deconstruction, evaluation, or review, thinking that even though they only have one fifth of the experience, knows little to nothing of her project work in detail, they must though have the knowledge to report on the woman's work better than she can.
She (as the lead scientist): To report on my findings of the project work I have been completing for the past month,

He (as the apprentice): <interrupting> the results show... bladibla…

Her peers: rolling their eyes, internally thinking (there he goes again, mansplaining...what a narcissist!)
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To mansplain is for a man to talk to a woman in a condescending tone that implies the man thinks of himself as smarter or superior in some way to the woman which he is not. Some people will use this term unnecessarily when a point they made has been proven incorrect and they have nothing else to say, but this is not, in fact, the correct use of the word. It is only correct to say a man is mansplaining if they have interrupted a woman or is explaining something to her which she did not ask him to explain or she has more experience on. An argument is often not a correct time to use the term “mansplain”
How “mansplain” should be used in a sentence:

Female Doctor: “Kyle, I have been working as a doctor for fifteen years, I didn't ask you to mansplain to me how the digestive system works.”

How “mansplain” should not be used in a sentence:

Man winning an argument: “This is how feminism becomes a thing that is mocked and ridiculed in our society. Don’t let this happen and please use words correctl-”

Woman, losing the argument: “Ugh, don’t be such a sexist. I didn’t ask you to mansplain it to me”
by spuder mun August 13, 2019
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To explain in a condescending, oversimplified, and often inaccurate manner, without regard to the fact that the explainee knows more than the explainer, usually done by a man to a woman.

Not all condescending explanations are mansplaining; the term does not apply when the man in question is indeed more knowledgeable about the topic than the woman.

Mansplaining usually occurs on the topic of sexism, feminism, or gender inequality, but not always. For example, a male programmer could mansplain coding to a woman, despite the woman having more qualifications and writing better-quality code.

Related terms include whitesplain, straightsplain, and cisplain. The overarching thread is someone privileged explaining something to someone less privileged, about a topic the explainer knows less about.
A: “Stop mansplaining. You have no idea what it feels like to be subjected to sexism.”
B: “Feminists are ridiculous! Mansplaining is when a man’s point is discredited just because he’s male, not because he’s wrong!”
A: “What the hell, did you just mansplain mansplaining to me?”
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Mansplain is often referred to when someone extensively explains something that the other party already has knowledge of, often in a condescending manner. The term is a combination of the words "man" and "explain" due to the commonality of men doing this. However, it can be used more broadly than just with men. This term is a negative term and is usually used by women.
Person #1: So I'm picking up my new GPU on the way home from work, right, when some dude in the store decides that I don't know enough and mansplains how to build a rig from scratch.
Person #2: But wait, didn't you build yours? Isn't that your job?
Person #1: Yeah but the dude just wouldn't stop or listen. I had to lie about having an appointment so I could just go to the register.
by Mjrin July 13, 2017
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An attempt by men/boys to help women/girls and provide information they believe that the women/girls need. Usually, the intent it to be helpful, not condescending; however, the effect is condescending. As a result, a great deal of controversy and anger exists; as with many -isms, it is the effect and not the intent that results in the definition. In addition, with many -isms, those guilty of mansplaining react with anger, derision, and ridicule rather than considering it a teachable moment.
Male runner at the start line of a trail race, observing a woman drinking from a water bottle: "You know, you should be careful the amount of water you drink, so that you don't suffer from hyponatremia. It's a very serious problem that can lead to death."

Female runner: "Um, thanks for the mansplain. I have a degree in exercise science, so if you'd like more information on that subject, I can help you out. "
by lynnsdaughter August 17, 2016
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