You are likely to encounter a fair bit of new terminology whilst walking the TA (Te Araroa [Trail]). Most of it originates from well-established US thru-hiking trails such as the AT (Appalachian Trail) and PCT (Pacific Crest Trail). The most common phrases are listed below.

SoBo: South-bound (the usual direction to walk the TA).
NoBo: North-bound (walking against the grain, more common in the South Island).
Purist: Someone who intends to walk the entire trail with no exceptions or shortcuts.
Efi (slang): Every Fucking Inch(er) - a different way to describe a purist.
Zero day: A rest day where zero progress is made on the trail.
Nero day: A nearly zero day, i.e., made a little progress on the trail but had a significant rest.
Resupply: Topping up of consumables (food, fuel, etc.) in preparation for the next section of the trail.
Gram weenie: Someone who is obsessed with ultralight gear.
Base weight: The weight of your pack plus all non-consumable gear. Excludes what you generally wear every day. Base weight is often discussed and compared amongst gram weenies.
Hiker hunger: An insatiable hunger that remains even after a big feed - often occurs after a few weeks on the trail. You can experience hiker hunger over many consecutive days.

For more thru-hiking terminology, go here.