子, or zĭ, is the Chinese scoring unit, referring to board points (literally "stones", or "pieces"). Roughly spoken, each point of the board counts to the color which is agreed to have conquered it.
The score in Chinese scoring then is given in relation to neutral (i. e. to the mid-count, 180.5 on a 19x19). This gives a result like, Black "wins by 3.5 zi ", where the Japanese would say, Black "wins by 7 moku".
People who are solely used to either way often omit the unit they are referring to, or replace it by the ambivalent term "points". To disambiguate the issue, it is a good habit to state the count together with "zĭ" or "moku", respectively.
Aside from the mere units, Chinese and Japanese scores can really differ though, since they are based on a different evaluation of the board position.