Truncation is like a wildcard. Added to the stem of a word, it will find that stem plus anything that comes after it. The symbol used to truncate a word depends upon the index, database, or Web search engine you are using.
psychol? will return records on psychology, psychological, psychologist.
? is used as the truncation symbol, for example, in AlleyCat.
environ*will return records on environment, environments, environmental.
* is used as the truncation symbol in MasterFILE & and Academic Search Premier.