1. What does FOS stand for?

Full of s***


Someone who thinks you're FOS thinks you're "full of s***." This acronym is used to call out people who are lying or ignorant.

S*** is a vulgar synonym for "feces." As slang, s*** is also used to mean "lies" (implying your words are comparable to s***). If someone says you're FOS, they think you are lying incessantly - either on purpose or out of ignorance.

FOS can also be used to call out exaggerations. For example, if your friend says they caught fifteen three-foot bass yesterday, you can pretty safely respond with "You're FOS."


Brandon's absolutely FOS. No way he opened a foil Charizard

A man who is FOS

Related Slang


Updated March 18, 2021
2. What does FOS stand for in online chat?

Feat of strength

When discussing tasks that require might or stamina, FOS stands for "feat of strength." You're most likely to encounter this acronym in gaming chat, when a gamer is discussing a task that will require all their power and skill to complete.

However, you might also encounter FOS in regular online chat sessions, when chatting with someone who just accomplished a difficult task. That person may refer to completing their task as a FOS.


It was quite the FOS to babysit all four of their kids last Friday night!
But I'm sure they enjoyed the night to themselves

A real FOS

Related Slang


Updated October 3, 2023
3. What does FOS mean online?

Freedom of speech

When referring to the freedom to speak their minds online and in texts, people may use "FOS." For example, your friend may post in a forum, "Thankful for FOS that allows us to exchange ideas and opinions freely no matter how weird they might be."

People often use FOS politically on social media when they think someone or something infringes upon their speech. For example, a person may post on Facebook, "I think it's scary what they are doing to our FOS on this site. So many of my friends say they no longer see my posts."


I'm so thankful we allow FOS in our country!
Agreed! We have to protect it, tho!

Everybody has FOS, including vegans

Related Slang


Updated October 12, 2023
4. What does FOS stand for?

Figure of speech

An acronym that refers to a commonly used phrase that means something other than its literal interpretation, such as "butterflies in my stomach" or "I'd give my left arm for that."


I was trying to explain to my online friend from Asia that "piece of cake" was just an FOS

Related Slang


Updated May 4, 2018

FOS definition by

This page explains what the acronym "FOS" means. The various definitions, examples, and related terms listed above have been written and compiled by the team.

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