Truncation allows you to get more out of your search term.
Often times the databases do not understand plurals.
A search of OIL SPILL might give you 70 Results.
A search of OIL SPILLS might give you 186 Results.
However a search of OIL SPILL* will give 203 Results.
Truncation Symbols Vary:
Library Catalog and Most Databases is: * (asterisk)
Lexis Nexus is: ! (Exclamation Point)