Istikhārah is literally to seek Khayr, to seek good.
from khayr = good
to seek good
Istikharah means to seek guidance/good from Allah I by means of salaah and du’a.
seeking Allāh’s counsel, advice, guidance
Istikharah is similar to what the Queen of Sheba did with her advisers when she heard from the Prophet she "consulted" them
'O Allah, I seek Your guidance [in making a choice] by virtue of Your knowledge, and I seek ability by virtue of Your power, and I ask You of Your great bounty. You have power, I have none. And You know, I know not. You are the Knower of hidden things. O Allah, if in Your knowledge, this matter (then it should be mentioned by name) is good for me both in this world and in the Hereafter (or: in my religion, my livelihood and my affairs), then ordain it for me, make it easy for me, and bless it for me. And if in Your knowledge it is bad for me and for my religion, my livelihood and my affairs (or: for me both in this world and the next), then turn me away from it, [and turn it away from me], and ordain for me the good wherever it may be and make me pleased with it."
The Prophet added that then the person should mention his need. [Sahih Bukhari]