What is Nerfing?

Hi,
I apologize in advance for my ignorance, but what the heck is "nerfing" a ship? I see it all the time, but have no idea what it means. Forgive me, I'm old...I cut my gaming teeth on Pong, Moon Lander, and Hemorrhoids...or was it Asteroids? 

Please help.

I didn't find the right solution from the Internet.

References:
forum.worldofwarships.com/topic/154321-what-is-nerfing/
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Thanks