Infact its not a technology but Emission Standard adopted by European Union. Current version being followed in EU is Euro V which has been launched in 2009
Threshold for diffrent exhaust particals may vary depedning on type of vehicle like bikes, Passenger Cars, Commercial Vehicles Light wieght & Heavy. etc.
Most of engines designed before ~1990s are not following any emission stadard but can complaince Euor II standard with help of some minute changes. some of the the most common practices are,
1) Improvement in carbeuration sytem which directly increases Fuel efficency & decreases emission level of hydro corbons & Green house gases.
2) Addition of ASV ECU (Air Suction Valve type Emission Control Unit)which helps oxidizing Hydro Corbon & Green House Gasses right after they exits from Engines Exhaust ports & reduces emission harmness.
Some of the bikes luanched in Pakistan after 2000 were already Euro II complaince due to improved carbeuration & efficient combustion system Like Suzuki Sprinter, Honda CD 100 Suzuki GS 125/150 but they are not specificaly mentioning it while selling there products.
In 2008 Ravi Introduces Strom 125 which was equiped with ASV ECU & it was a new thing in Pakistani market & due to their affliation with famous Eurpeon Brand Piaggio they speicfcally mention Euro II acronym on their product.
From marketing perspective it was a attraction for coutomer & plus point for seller to have Euro II tag on the product so after the Ravi, Atlas Honda tagged their CD100 with Euro II & later Suzuki also realizes to have that tagged on their Bikes coz their products may already have complaince with this standard.
Currently Storm 125 & CG Dlux (2010 onwards) are having ASV type ECU.