Is "sb." a commonly accepted abbreviation? What does it mean?

What does sb. mean? I keep seeing it certain posters' questions and I'm not sure what it's supposed to stand for — the word something, my initial guess, doesn't have a 'b' in it. So my questions are: Is it a known abbreviation? What does it mean?

sb. is used as abbreviation for substantive, which grammarians use as a basic term form for noun. This is an old practice from the Latin days. n is used to denote proper nouns in such cases.

For example, in "What does “pull sb. out of the hat” mean?", sb. is used as a placeholder for a noun.

Could it just be the abbreviation of somebody ? Here is an official definition.

But there are also many possible contenders.

Edit
In case your question refers to the previously submitted question "what does pull sb. out of the hat mean ?" then the answer is definitely "somebody".

For instance in my Oxford Phrasal Verbs Dictionary, I can read: