What is 2⁷, and what does it signify?

128 — the number of code points in 7-bit ASCII, and one past the max of a signed byte (−128…127).

Chunk 128 → 12 · 8 → tuna · ivy: picture a tuna wrapped in ivy. 128 is where a single signed byte tops out at +127 and where standard ASCII (0–127) lives.