What is the difference between Ruach haKodesh and Shekinah?
Is there a difference between the two concepts or are they exactly the same?
Shekinah is the Divine Presence - meaning how God reveals himself in this world, while as Ruach HaKodesh is divine state of a PERSON who can reach higher spirituality than general public.
Don't be confused and DO NOT translate Ruach HaKodesh as Holy Spirit to get something like 1/3 of the Trinity in Christianity.
Jewish Encyclopedia ('Ruach HaKodesh') says:
What the Bible calls "Spirit of Yhwh" and "Spirit of Elohim" is called in the Talmud and Midrash "Holy Spirit" ("Ruaḥ ha-Ḳodesh." never "Ruaḥ Ḳedoshah," as Hilgenfeld says, in "Ketzergesch." p. 237). Although the expression "Holy Spirit" occurs in Ps. li. 11 (LXX. πνεῦμα τὸ ἅγιον) and in Isa. lxiii. 10, 11, it had not yet the definite meaning which was attached to it in rabbinical literature: in the latter it is equivalent to theexpression "Spirit of the Lord," which was avoided on account of the disinclination to the use of the Tetragrammaton (see, for example, Targ. to Isa. xl. 13). It is probably owing to this fact that the Shekinah is often referred to instead of the Holy Spirit. It is said of the former, as of the Holy Spirit, that it rests upon a person.