Kia ora is a Māori language greeting which has entered New Zealand English. It means literally "be well/healthy" and is translated as an informal "hi" at the Māori Language Commission website Kōrero Māori. The New Zealand Ministry for Culture and Heritage website NZ History lists it as one of 100 Māori words every New Zealander should know, with a definition "Hi!, G'day! (general informal greeting)".
It also signifies agreement with a speaker at a meeting, as part of a culture which prizes oratory as infotainment. Other Māori greetings, "Tēnā koe" (one person), "Tēnā kōrua" (two people) and "Tēnā koutou" (three or more people), are also widely used.
Likewise, "kia ora" can follow a similar pattern to address different specific numbers of people. By itself, it can be used to address any number of people, but by adding "koe" (i.e. "kia ora koe") one can specify a greeting to a single person; "kōrua" (two people); "koutou" (three or more people); and by following with "tātou" one addresses all the people present, including the speaker themself.
The word is similar to the word "kia orana" found in some Pacific Island languages and with a similar meaning.
Jennifer Garner once used the greeting in an American infomercial targetted towards New Zealanders. The incident was notable because of her phonetic (and incorrect) pronunciation (kee-ya or rah) creating a backlash against incorrect use of Maori customs.