A tahua is, it seems, a kind of plaza for gathering the people:

Ahu Haga O Hônu:

"... The central portion of this wall projects outward towards the sea to form a platform or stage on which the statues were erected. This salient corresponds to the body of the ahu and the two lateral walls may be considered the wings. A little below this stage the main body of the construction, made of piled-up stones, slopes inland, extending into a long, slanting surface (tahua) which stops at a low row of slabs. The approach to the slope is sometimes paved with big boulders which continue onto the large surface (tahua) ..." (Métraux)

Tahua

Sloping stone surface of ahu. Vanaga.

OR. Tahua mimi, bladder. Fischer.

T. Board, plank. Fischer.

When king Hotu Matua arrived with his double-canoe to the southeast corner of the island - legend says - the lashings were liberated and he took the righthand way around Poike to land at Anakena, while the other canoe (with his sister Ava Rei Pua onboard) took the lefthand (shorter) way to Anakena:

"... Because of supernatural interference, the sister canoe comes in second and has to land to the west at Te Tahua, where the shore is becoming increasingly more rocky, or even farther west (Hanga Ohiro, TP:35; Hanga-o-hio, ME:60).

It is an open question whether or not the selective contrast in local names, Hiro Moko vs. Hanga O Hiro, represents an extension of the contrast based on sex and rank or whether, in this case, a different system is in operation.

Based on its place of birth and the landing site, the child of Ava Rei Pua, whose name is not mentioned, is related to that segment of the 'second list of place names' that has to do with the moon.

Figuratively speaking, the child of the sister of the immigrant king is associated with the narrow crescent of the new moon ..." (Barthel 2)

The name Tahua for the rongorongo tablet A presumably alludes to the landing place of Ava Rei Pua. At the beginning of the text (i.e. the first line on side b) we can see glyphs representing birth:

The first glyph has the function to inform where to begin the reading (on side a or on side b) and the second glyph shows light emanating from a new moon crescent.