A SNOT brick has one or more outward-facing studs on the side.
The outward facing studs on many SNOT bricks are hollow, which allows you to attach a Bar element inside the hole. This is another connection type which you can use to build better models.
33861×1×⅔ Stud 1-side, Ø1 Rounded End
40701×1 Brick, Headlight
870871×1 Brick, Stud, 1-side
479051×1 Brick, 2-studs, Opposite Sides
266041×1 Brick, 2-studs, Adjacent Sides
47331×1 Brick, Studs 4-sides
329521×1×1⅔ Brick, Studs 1-side
112111×2 Brick, Studs 1-side
521071×2 Brick, Studs 1-side
304141×4 Brick, Studs 1-side
228851×2×1⅔ Brick, Studs 1-side
807961×2×1⅔ Brick, Studs 2-sides
673291×2×1⅔ Brick, Studs 3-sides
45951×2×⅔ Studs 2-sides, Antistud