D stands for DIGITAL
T stands for TWIN
S stands for SPARK
I stands for IGNITION
The Dtsi is the advanced spark plug ignition system introduced by bajaj in pulsar 180. this is the best fuel ignition system ever used in bikes, in this the two spark plugs are situated on cylinder wall as they at 45 degree agle. so when half charge packet(Air fuel ratio) gets burn by 1 spaqrk plug and another one with 2nd spark plug, this gives better fuel burn at higher speed ratio of the piston.
Well i am here attaching image of Dts-si engine which is advanced then Dtsi but u can see the sparkplug arrengment in that same like dtsi.