Son of man in the Bible is used in the following senses:
(1.) Denotes mankind generally, with special reference to their weakness and frailty (Job 25:6; Ps. 8:4; 144:3; 146:3; Isa. 51:12, etc.).
(2.) It is a title frequently given to the prophet Ezekiel, probably to remind him of his human weakness.
(3.) In the New Testament it is used forty-three times as a distinctive title of Jesus. It emphasizes that he had human as well as divine nature.
From Easton's Bible Dictionary (1897)
It must be remembered that when interpreting the Bible one cannot exclusively rely on English translations. Thus, "son of man" in Job 25 is "ben adam," and "son of man" in Psalms 144 is "ben enosh."
Geza Vermes (1924-), professor emeritus of Jewish studies at Wolfson College, Oxford, has argued that "the son of man" in the Gospels is unrelated to these Hebrew Bible usages. He begins with the observation that there is no example of "the" son of man in Hebrew sources. He suggests that the term originates in Aramaic, "bar nasha." Based on his study of Aramaic sources, he concludes that in these sources and in the Christian Bible, "son of man" is simply a synonym for man, and a substitute for the indefinite pronoun ("one"). Based on context, he claims that one should translate "bar nash(a)" as "someone," "anyone," or "I." He further argues that "son of man" is in no way a "title."
Although the Aramaic "bar enash" can be translated generically, e.g. as "somebody" or "anyone", the expression would readily be recognized as a title if it were used within a Hebrew sentence.
See Randall Buth, "A More Complete Semitic Background for bar-enasha 'Son of Man'" in Craig Evans and James Sanders, eds. The Function of Scripture in Early Jewish and Christian Tradition (JSNT Suppl 154) Sheffield Academic Press, 1998: 176-189.