Qiyam

Tahajjud (ta-hajj-od), also known as the "night prayer" is a voluntary prayer, performed by followers of Islam. It is not one of the five obligatory prayers required of all Muslims, yet still, Muhammad is recorded as performing it many times and encouraging his companions to offer it for its many rewards and benefits.
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Standing erect (during prayers)

Useful information:
OBLIGATORY ACTS RELATING TO PRAYERS
There are eleven obligatory acts for prayers:
(i) Niyyat (intention).
(ii) Qiyam (standing erect).
(iii) Takbiratul Ehram(saying Allahu Akbar while commencing the prayers).
(iv) Ruku' (bowing).
(v) Sajdatayn (two prostrations).
(vi) Qiraat (recitation of Surah al-Hamd and other surah).
(vii) Zikr (prescribed recitation while bowing and prostrating).
(viii) Tashahhud (bearing witness after completing the prostrations of the second unit).
(ix) Salam (salutation).
(x) Tartib (sequence) (xi) Muwalat (to perform the different acts of prayers in regular order without stop).

Qiyam is the standing during the Salat for recitation of Suratul Hamd and the second Surah, and the standing after the Ruku'.