Amidah

The Amidah (עמידה, "standing") is one of the two main prayers of Judaism. It has that name because people say it standing up. Jews say it at every prayer service of the year.

It is also called Shemoneh Esrei (שמונה עשרה, "eighteen") because at first the weekday version of the prayer had eighteen blessings. (It now has nineteen.) In the Talmud, it is called Tefilah (תפילה). This simply means "prayer". It has that name because it is so central to Judaism.