"Maximum Password History Entries" is a GAM Security Policy property which allows to store the list of the last passwords which a user used to have, in order to avoid repeating any of these passwords when he defines a new one.
GAMExampleEntrySecurityPolicy web panel (located in GAM Example folder) is an example where this property is used.
The way to use it in GeneXus code (by using the GAM API) is the following:
&SecurityPolicy.MaximumPasswordHistoryEntries = &MaximumPasswordHistoryEntries
For example, if "Maximum Password History Entries" = 5, when the user changes his password, he cannot define a password which is in the list of the last 5 passwords he used to have.