and is almost always a conjunction. Really, the answer could stop here.
As @RonaldSole's link demonstrates, a dictionary definition for and may mention that it can also act as a noun or a modifier when referring to the operation in logic or electronics: an AND gate; we combined the three inputs with two ANDs. However, this is a very specialist use.
When @KillingTime said, in a comment on your other question, that and wasn't being used as a conjunction, it had nothing to do with the meaning of the specific word and. Absolutely any word can be used in various ways not found in its dictionary definition. For example:
- As a noun, meaning "an instance of the word":
I wrote a sentence with fifteen ands in a row. (Shor may have an algorithm, but I have more ands!)
Often, we would put the word in italics or quotes, but we don't have to.
- As an interjection, for emphasis:
You're never satisfied! And, and, and, you always want more.
Note that these possibilities are available for all words, and they have nothing to do with the meaning or part-of-speech of the specific word and:
There are too many talls in this paragraph.
I think you should delete the angrily in that sentence.
Should I put a comma after the first the in the name of the band The The?
He said the food was too spicy. Spicy! What does he know about cooking?
He asked if she was a manager. A! She's THE manager!
In summary: unless you're discussing Boolean logic, and is always a conjunction. But every word in the language can be used in ways not covered by its dictionary definition.