What is the Spirit Referred to in Ecclesiastes 12:7?

In Ecclesiastes 12:7 Solomon is inspired to write the following statement:

"Then the dust will return to the earth as it was, and the spirit will return to God who gave it. (Ecclesiastes 12:7)

This is speaking of the time of a person's death, at which time a "spirit" is said to return to God. What is the spirit referred to in this scripture?

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