Mansplaining is when a man is explaining something to a woman like she is stupid (because she is woman). It’s a popular slang term lately.
Classic examples of mansplaining:
(1) In a team meeting, the lead software developer (a female) is explaining some technical aspect of a project. A male team member interrupts to explain it to her, even though she has more expertise in that area😒
(2) A gym-bro explaining to a female bodybuilder how to gain muscle🥴
The gerund is mansplaining: I’m sick of his mansplaining.
The verb is mansplain: Don’t mansplain diet and training to me.