The word romanization refers to the use of the Latin (Roman) alphabet to phonetically represent the sounds of a language which does not normally use the Latin alphabet. Thus, pinyin is a form of romanization of Mandarin Chinese.
The following are all systems of romanization for Mandarin Chinese:
This wiki does not extensively cover other forms of romanization besides pinyin, because pinyin is all that most learners need nowadays. Please see Wikipedia's article on Romanization of Chinese for more details on other romanization systems.
The following are not considered romanization because they do not use the Latin alphabet, or do not use only the Latin alphabet: