Exactly what is a dc to dc charger?

[shadowmoss]

I have a degree in this stuff (a few decades ago), and I've been reading and interested in the electronics side of things for several years now.  I know how things work.  However, I'm finding that things that I know what they do now go by different names.  I have come to the (possibly incorrect) conclusion that a dc to dc 'charger' is what I know as a battery isolator that is put between two batteries to keep either one from drawing the other down past a set voltage, but sharing voltage above that point.  Am I right or wrong?  This term seemed to take over discussions a couple of years ago, and I never hear the term isolator now.