also: エータ
noun
The Greek letter η (Η), used in mathematics, physics, and engineering. In Japanese, typically read as イータ, sometimes エータ.
物理学では、ηは効率を表す記号としてよく使われる。
In physics, η is often used as a symbol for efficiency.
この式のηに数値を代入してください。
Please substitute a numerical value for η in this formula.
From Greek letter η (eta). The reading イータ reflects modern Greek pronunciation, while エータ is based on classical or English-influenced pronunciation.