Eunhyuk was born Lee Hyuk-jae in Seoul, South Korea. He has an older sister Lee So-ra. Raised in a family that struggled financially, he was interested in street performing as a child. Inspired by the likes of H.O.T's Jang Woo-hyuk, Michael Jackson and singer-dancer Yoo Seung-jun, Eunhyuk trained himself at a young age.

On 16 December 2011 Eunhyuk and Donghae released digital single Oppa, Oppa, where they first performed it at Super Junior's Super Show 4 Seoul concert on 19 November 2011. This marks the first release of their collaborations. The single was also released in Japanese with an original Japanese music video on 4 April 2012. On the day of its release, it reached number two on Oricon Daily Chart with 42,114 copies sold. While also preparing for Super Junior's first world tour Super Show 4, the pair held a fan meeting, Premium Mini Live Event, in support of the single on 11 April at Shibuya-AX, Tokyo.  Eunhyuk is MC for MBC every1's Super Junior Foresight, along with fellow members Leeteuk, Kyuhyun, Yesung and Shindong. From 23 March 2012, he took over as MC for the last three live shows of singing-survival program Great Birth 2, better known as MBC Star Audition, on MBC. As of the 10 April 2012 broadcast, following the change in MCs and the departure of Shindong from Strong Heart, the show was re-vamped with Leeteuk and Eunhyuk billed as two of the 'six-fixed guests'.  In June 2012, Eunhyuk reunited with his Super Junior bandmates for their sixth studio album, Sexy, Free & Single released on 4 July. On 21 June 2012, the first teaser photo of Eunhyuk was released showing him in a white shirt, blue jeans, styled with a mullet-like hairstyle and blindfolded with white and pink flowers. In October SM Entertainment and Hyundai partnered up to release the "Maxstep" featuring Eunhyuk and other SM artists Super Junior-M's Henry Lau, SHINee's Lee Taemin, EXO-K's Kai, EXO-M's Luhan and Girl's Generation's Hyoyeon. The group became the official dance unit; Younique Unit. The official cover of Zedd's Spectrum was released via SBS Gayo Daejeon held on December 29, 2012, with Eunhyuk featuring. The single was performed by the members of SM The Performance and also included Donghae, along with TVXQ's Yunho, Shinee's Taemin and Minho and EXO's Kai and Lay.

Using a quote from the above article, answer the following question: What was Oppa Oppa?
Eunhyuk and Donghae released digital single Oppa, Oppa,