"Delendum" is the gerund version of "delere", and the gerund can be used in two contexts with completely different meaning.
The first is the simple gerund, where it basically means that the verb is the complement of another verb/noun/… (so "verb/noun" + "of" + "verb + ing" or "verb/noun" + "to" + "verb"), for example "tempus legendi" (the time to read/of reading), "cupio manere" (I wish to stay).
The second is what is called the gerundive, where the gerund form is not only declinated, it is also accompanied by the "esse" verb.
The most famous example is "Carthago delenda est".
In this case, the verb takes on a dimension of necessity and obligation, and therefore "Carthago delenda est" means "Carthage is having to be destroyed", literally, and therefore "Carthage must be destroyed".
Edit: note: the terms "gerondive" and "verbal adjective" are perhaps incorrect… Indeed, having studied Latin in Belgium in a French-speaking school, I only know the French terms, i.e. "gérondif" and "adjectif verbal". I hope the terms I used are somewhat correct translations…
Edit 2: thanks UE_R&D for the correct terms in English!
This post has been edited by Pace : 15 December 2006 - 11:59 AM