I know that SNOT means "Studs Not On Top", but I've also seen "SNIR" used, often in the same context as SNOT, but clearly different - what does it mean?
SNIR is the abbreviation for "Studs Not In a Row" - almost self-explaining, but for more information, take a look at this small article.
[...] very useful on walls and other things. In Lego, studs (nubs, dots, etc.) are in a row, and a straight one. Using SNIR makes studs be in zigzags or diagonal lines. [...]