Whati means "to break," as in breaking a stick.

In traditional Maori culture, whati came to mean making an unintentional break in a karakia.

Today some people use the name "whati" for a mistake when singing the words of waiata.

A verse of a karakia was properly recited "kawa rukuruku," on a single breath without pause. During recitation by two persons, pupils were taught the precise word upon which one reciter had to take over from the other in order to maintain continuity of sound.

Although care to avoid breaks for breathing probably originated with karakia, it is also characteristic of other forms of singing such as waiata. Mervyn McLean says that when he began his field work in 1958, mistakes in waiata singing were regarded with dismay by many singers, especially if there was a complete breakdown. Performance continuity in waiata singing was achieved by the use of end-of-line leader solos, known as hiianga, during which the other singers in the group could take breath.

Whati-inga refers to modifying the pronunciation of word to make it fit the music, for example where a diphthong is sung to two syllables instead of one, where a short vowel is sung long, or where stressed syllables appear in the wrong placess.

In the times before pens and paper, Polynesian history, genealogy and other wisdom was conveyed by chanting. And it is still done: ten years ago I heard a couple of men at Moawhango recite their genealogy together for ten minutes or more without any hesitation, a prodigious feat of memory. So avoiding mistakes was and still is very important for those chants.

The traditional way of composition was for a group to work at a waiata for a couple of weeks or more until all were happy with it, and for each of these older waiata that were probably composed this way, I have found only one version.

Tarakihi, 1600s locust dream chant.
Po! Po!, 1600s story of kumara origins.
E Pa To Hau, 1865 lament for stolen land.
Te Kiri Ngutu, 1870s protest at land seizure.
Te Ope Tuatahi, 1916 WWI anthem.
Karangatia Rä, 1919 welcome for returning warriors.
Poropeihana, 1927 protest of alcohol prohibition.
Arohaina Mai, WW2 farewell to departing soldiers.

But a lot of shorter emotive waiata have been thrown together in a day or so by individuals, usually for a specific occasion, and many of them have developed variations as others have improved the lyrics (Haere ra), improved the rhythm (Tutira mai), removed bad verses (2nd verse of Tari nei taru kino), or modified the meaning to suit changed situations (Matangi and Ka Mate)

Toia Mai, 1400s boat-hauling chant. Many variants.
Ka Mate, 1500s boat-hauling chant praising the captain. Many variants in use until WW2.
Paikea, 1600s? the whale rider. Two rangi and two regional variants.
Hine E Hine, 1907 lullaby. Several variants.
He Püru Taitama, 1910 courting song. Several variants and additions.
Pokarekare Ana, 1912 love song. Many variants, plus Korean, Indonesian, Norwegian and Irish.
Tipirere, WW1 love song, Long Way to Tipperary. A Ngati Porou variant keeps this song alive.
Hoea Rä Te Waka Nei, to support WWI soldiers. Many variants, and changes of meaning.
Ho--ki Hoki, WW1 lament. Seven variants.
E Pari Ra, WW1 lament. Several versions.
Po Atarau, Now is the Hour, 1920. Umpteen variants - the folk process at work here!
Me He Manu Rere, 1920s lover's lament. Three or four variants.
Matangi, 1924 steamship journey. Nine distinct variants 1920s to 1980s,
                        marking the drift to the cities, away to WW2 and migration to Australia.
He Putiputi Koe/Pae, 1926 love song. Two variants.
Ma Wai Ra, 1933 call for a new leader. Several regional variants.
Tomo Mai, 1946 welcome for returning soldiers, changed to Hoki Mai for tourists in Rotorua.
Marie Te Po, Silent Night, different Maori translations by different Christian denominations.

Before learning to sing a waiata, it is good to check the original version, or a modified version that accurately conveys the meaning of the song. A lot of mistakes have occurred when someone has heard a song and written it down on a song sheet or the internet without checking the meaning of what was written.

Here are some Whati I have found.

Me He Manu Rere wrongly written as Mehe Manu Rere.

Ehara I Te Mea wrongly written as - E Hara I Te Mea, completely changing the meaning!

Te aroha - written as Tea roha.

The second line of "E Rere Taku Poi," Nga iwi o te motu, (the people of the island) has been incorrectly spread on the internet as Nga riri o te motu, and this has been "corrected" as Nga riri o te moana (the anger of the ocean), which then mutated to Nga rere o te mana (the flight of the spiritual power ???)

Hoki Mai e tama ma ki roto, ki roto - had become Hoki mai e tama ma, teraki teraki

Terina ends  Ma tau aroha e rau o taku titapa e.
        It is not Ma ta aroha he wawata o taku tipapa e
                or Matou aroha he wawa ta taku titapa e
                or Matou aroha e rou o taku ti tapa e
                or Ma ko aroha, e rongo taku e tama e

He Kakano Ahau has the words
I am a seed, An ornament of grace, Ki hea ra, Taku reo. That you may know.
But it was commonly being sung wronly as 
I am the seed, An ornamental grace, I hea ra, Toke reo. That you they know.

Notice that the currently popular version of Ka Mate about Te Rauparaha's escape, that uses Hupane, kaupane -  up a step, up a second step - is a modification of an earlier "Maui slowing the sun" peacemaker version, U pane, u pane - strike the head, strike the head - which in turn is a modification of an even earlier voyaging-waka-hauling chant, Upane Kaupane - side by side, keep together. I think this boat-hauling version and Toia Mai were both brought from Tahiti.

Ka Mate is also used as a longer post-coital wedding night chant Kikiki Kakaka; with the same words but changed meaning. The Ka Mate version that Te Rauparaha and others actually composed at Kawhia ten years after his escape is a major modification of the wedding night chant.