Another of my favorite definitions from the Bible Dictionary.
Dreams: One of the means by which God communicates with men (link).
Peter quoted Joel in this respect:
And it shall come to pass in the last days, saith God, I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams: (Acts 2:17)
President Hinckley quoted Joel too:
The era in which we live is the fulness of times spoken of in the scriptures, when God has brought together all of the elements of previous dispensations. From the day that He and His Beloved Son manifested themselves to the boy Joseph, there has been a tremendous cascade of enlightenment poured out upon the world. The hearts of men have turned to their fathers in fulfillment of the words of Malachi. The vision of Joel has been fulfilled wherein he declared:
“And it shall come to pass afterward, that I will pour out my spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions:
“And also upon the servants and upon the handmaids in those days will I pour out my spirit.
“And I will shew wonders in the heavens and in the earth, blood, and fire, and pillars of smoke.
“The sun shall be turned into darkness, and the moon into blood, before the great and the terrible day of the Lord come.
“And it shall come to pass, that whosoever shall call on the name of the Lord shall be delivered: for in mount Zion and in Jerusalem shall be deliverance, as the Lord hath said, and in the remnant whom the Lord shall call” (Joel 2:28–32). (Living in the Fulness of Times, Oct 2001)