Q. What K10 (K & 10 separately) stands for

Hey it's a nice question. The name is derived from the engine this car uses. The main difference between Alto K10 and Alto 800 is the engine. The engine belongs to Maruti K series i.e K10B so probably Maruti has named the car. K stands for the K series motor and 10 for it's having a 1 liter engine. Similarly swift used K12 engine and it's a 1.2 liter 4 cylinder. Hope this address your concerns

Please understand my answer. The engine is the same except the CC and tuning which is what differenciates the two engines.

K - K series engine, 10 - One Litre Engine. K10 is similar to the 800cc engine but tuned for better performance.