ICOCA Card: 

A Convenient and Versatile IC Card for Exploring Japan

ICOCA (イコカ / Ikoka) is a smart card—issued by JR West  and mainly sold/used in Kansai region (関西)—has the following characteristics: 

Note that there are other stored-value cards such as Pasmo, Suica, etc. Since March 2013, major 10 different IC cards were standardized and become inter-operable.[1,2] In my own experience, I was able to use ICOCA card in both Tokyo and Hakone areas on both trains and buses without issues except once when I tried to charge my ICOCA card at Hakone-Yumoto Station via the vending machine. My ICOCA card was not recognized by the machine. However, I was able to get it recharged through the "Fare Adjustment" personnel at the station.