A terabyte is an amount of computer storage — the size of a hard disk, a memory card, a cloud account. It sits one step above a gigabyte: 1,024 gigabytes, or in the rounder way most people count, a thousand gigabytes, which is a million megabytes. That is the honest muddle at the heart of the word. Computer engineers count in powers of two, so for them a terabyte is 1,024 gigabytes; disk makers count in plain thousands, so the 1 TB disk you buy shows up on your computer as about 931 GB, and every year people think their new disk is broken when it is not. Some careful writers use **tebibyte (TiB)** for the 1,024 version to keep the two apart, but almost nobody says that out loud. In real life a terabyte is roughly a quarter of a million photos from your phone, or a few hundred hours of video — big enough that ordinary people only started needing the word in about the 2010s, and small enough that a phone will get there soon. Written short as **TB**. Say it TERR-a-byte.

TB、兆位元組（台灣多半直接講「一 T」「兩 T」，例如「這顆硬碟兩 T」）。注意台灣的「兆」在資訊裡指的是 10¹²，跟一般說的「兆」意思不同，所以說 TB 最不會誤會。