When a mathematically capable person explains a math problem to a less mathematically capable person, typically in a manner regarded as condescending or patronising. Like mansplaining, except that it actually exists.
Math HL student: "Uh, you can't get the square root out of a negative number. Unless you're using irrationals"
Math studies student: "Stop mathsplaining to me!"
When you trap your life long formula one rival in order to explain every little detail about your race or quali session to them without a chance of escape.
When frustrated manly men go and flood the Urban Dictionary with their definitions of the word Mansplaining, because they know it better than the feminists, actually.
Greg is so pissed off because his professor didn't want to hear him explain her area of expertise to her in his opinion, so he went meta-mansplaining in UD and invited all his friends too. (See mansplaining )
When unsolicited advice or direction is given to a woman by a man in a condescending manner. The reasons typically being, the man does not believe the woman is capable of completing the task independently and must need guidance.
"You're not doing that how I would do it so I'm going to bother you with my directions and opinions even though I am in no way a superior and you did not ask for clarification. There is no way you are capable of doing this by yourself and must be ignorant so you have to rely on my constant guidance."