An acronym (首字母缩略词) is an abbreviation (缩写词) that consists of the first letters of the words in a phrase, and is usually pronounced as a word.

1. AIDS is an acronym for Acquired Immune Deficiency Syndrome.
2. NATO is an acronym for North Atlantic Treaty Organization.
3. Behold the Mobile Omnidirectional (全方向的) Neutralization (中立化、去武装化) and Termination Eradicator (根除者), or MONTE (蒙蒂). [S2E12, TBBT]

BTW和SMS之流则读作一串字母。

4. Here's a cheat sheet of SMS (Short Messaging System/Short Message Service) abbreviations: TBD: To be decided, TBA: To be announced, BTW: By the way, LMK: Let me know, NVM: Never mind.

但是[S4E14, TBBT]:
Sheldon: Yeah, I'm not familiar with the acronym "KMN".
Leonard: From the context, we think it means "kill me now."
英语好如Sheldon者，都认为K-M-N(读作三个字母)是个acronym.