"Pinyin" literally means "phonetic spelling". The system was developed in the Sovied Union in 1931, and a slightly revised version was in 1958 introduced as the official system to transcribe Mandarin Chinese in the Peoples Republic of China.
The system makes use of the Latin/Roman characters "A" to "Z" (minus "V") plus four types of accents that denote the tones of each syllable. Some European letters are used for sounds not entirely corresponding to the letters (e.g. "Q" and "X" are used for sounds that might be described as "tch" and "sch").
Most countries of the modern world tend to use this system when romanising Chinese today - only emitting the tones. In China, the system is used for road signs, maps, brand names, computer input, Chinese Braille, telegrams, semaphore, in dictionaries, when teaching Chinese and many other purposes.
Enter the romanisation for for a syllable in Mandarin Chinese according to Pinyin or Wade-Giles, and this glossary will give you the corresponding transliteration according to other systems!
Further reading:
Bopomofo,
Chinese phonetics,
hanzi,
tones,
Wade-Giles,
Zhuyin 
