Simplified Chinese is one of the two commonly used forms of writing Chinese languages. As its name shows, it is a more simple form of writing, compared to traditional Chinese.
Simplified Chinese was first put to public use in 1964 by the Chinese Communist Party under Mao Zedong, along with many other educational changes, in hopes that the majority of Chinese, then illiterate, would be able to read and write. The concept was one of many steps put forward to eventually change Chinese into a Japanese-like language, with a phonetic alphabet, similar to the Zhuyin system developed in 1912, which was replaced by Pinyin in China in 1958 but still used in Taiwan today. The second set of even more simplified Simplified Chinese was put into place first in 1978, then in 1984 and both times met with strong opposition because it created more problems due to the merging of too many characters with different meanings.
Simplified Chinese, although widely enforced and used today in China, have no solid proof of actually aiding in learning Chinese, while in Taiwan, Hong Kong, and in Chinese communities overseas, Traditional Chinese flourished with no literacy problems. It has raised issues in 2009 when a Chinese official Pan Qing-Lin, addressed the issue and proposed to abolish Simplified Chinese but was later rejected. see here.