Abbrevs can also have global definitions that are active in all major modes. The same abbrev can have a global definition and various mode-specific definitions for different major modes. A mode-specific definition for the current major mode overrides a global definition. You can define Abbrevs interactively during an editing session. You can also save lists of abbrev definitions in files and reload them in later sessions.
Some users keep extensive lists of abbrevs that they load in every session.
A second kind of abbreviation facility is called the dynamic expansion . Dynamic abbrev expansion happens only when you give an explicit command and the result of the expansion depends only on the current contents of the buffer. See section Dynamic Abbrev Expansion . After this command, no abbrev definitions remain in effect. This reads the abbrev itself using the minibuffer, and then defines it as an abbrev for one or more words before point.