Alt (regular alt key)
Alt Gr (angery alt key)
@elomatreb I have AltGr but it doesn't seem to do anything for me? 🤔 I didn't even realize it was something different until you said! 😮
@chevko It's used for accessing the third symbol on keys, the USA keyboard doesn't have a lot of them but e.g. on German keyboards € is AltGr + E and a lot of the punctuation ([]/{}) as well, since we need at least 4 extra keys for regular letters (umlauts and ß)

@chevko @elomatreb You can use it to make these useful symbols on Linux:
» and « with z and x
←↓→ with yui
… with . (as opposed to ...)
· with ,
– with -
| with <

Add shift to the mix:
÷ with .
× with ,
— with -
↑ with u
® and © with r and c
¥Ŧ with yt
›‹ with zx
⅛⅜⅝⅞ with 2567
™ with 8
± with 9

(tested on a German keyboard layout)