A general encyclopedia is a reference work that contains information on all branches of knowledge. Articles are arranged alphabetically, often by subject. The entries are typically short and provide an overview on the topic. An example of a general encyclopedia is Encyclopedia Britannica
In contrast, a subject encyclopedia is more focused and covers a particular area of information. The entries are typically longer in length and go into much more detail than a general encyclopedia and usually include references for further information. One example is Encyclopedia of philosophy / Donald M. Borchert, ed. (2005-2006).