It's actually a noun meaning "the truth" -- or to be more precise, it's the adjective "vērum", meaning "true", acting as a noun ("a true thing"). In Latin, there are three words that may be translated as "the truth":
* Vērum: The truth about a specific fact.
* Vēra: The plural of vērum. Refers to something rather less specific than vērum. For example, "In illā terrā nōn licet vēra dīcere" -- in that land it is not permitted to speak true things.
* Vēritās: Truth in a broad, general sense. A famous proverb: "In vīnō [est] vēritās".
The word "vērō" is related (ablative of vērum, but often more like a conjunction), which you will find in Chapter 16 and is used often from thereon. You will also often see the adverb "vērē" used to mean "truly" ("Dīvitēsne vērē sumus?" -- "Are we truly rich [or are we just imagining it]?"), though I don't recall this appearing particularly often, if at all, in Lingua Latina I.