Psi has two very different uses.

PsiPsi has有 two very different uses兩種很不一樣的用法。

In science and engineering, "psi" is a unit for measuring pressure — it stands for "pounds per square inch," and you'll see it most often when checking how much air is in a tire or a ball ("inflate to 32 psi").

In science and engineering在科學和工程領域，'psi' is a unit for measuring pressure「psi」是一個測量壓力的單位 — it stands for它代表 'pounds per square inch,'「pounds per square inch（磅力每平方英吋）」，and而且 you'll see it most often最常見到的情況 when checking how much air is in a tire or a ball是在檢查輪胎或球裡有多少氣的時候（'inflate to 32 psi'像「inflate to 32 psi（打氣到32 psi）」這樣）。

Separately, "psi" is also the name of a Greek letter (Ψ, ψ), used in math, physics, and other technical fields as a symbol.

Separately另外，'psi' is also the name of a Greek letter (Ψ, ψ)「psi」也是一個希臘字母的名字（Ψ、ψ），used in math, physics, and other technical fields as a symbol在數學、物理和其他技術領域被當作符號使用。

It's also sometimes used informally, especially in science fiction, to talk about "psi powers" — imagined mental powers like reading minds — though this fictional sense is much less exact and just borrows the Greek letter's mysterious feel.

It's also sometimes used informally它有時候也會被非正式使用，especially in science fiction尤其是在科幻作品裡，to talk about 'psi powers'用來說「psi powers（psi能力）」 — imagined mental powers like reading minds指像讀心術這樣想像出來的心靈能力 — though this fictional sense is much less exact不過這種虛構用法沒那麼精確，and just borrows the Greek letter's mysterious feel只是借用希臘字母那種神秘的感覺。