muff
n.— «Gone are the days when all capacitors were only measured in uFs and pFs (muffs and puffs as they are affectionately known).» —“Capturing the capabilities of ultracapacitors” Components in Electronics (U.K.) Sept., 2004. (source: Double-Tongued Dictionary)
Further reading
juicy noun. A person who illicitly carries alcohol in a water bottle. «Gwen Alexander, who’s been working at the Astoria pool for two years, confirms there haven’t been any issues with fighting this year but she said rule enforcement is...
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In the electronics context uF is microFarad (rather than “u” it should be the Greek letter mu – I don’t know how to type this on an English keyboard).
Hence “muff” is a colloquialism for microfarad. Whether it should really be regarded as a word or is just the author’s attempt at representing the way uF is often pronounced.
Similarly pF = pico farad.