Horn

Horn = King/Kingdom

Ram

Daniel equates the two horns of the ram with the kings of:
1) Media,
2) Persia.

Dan. 8:3 Then I lifted up mine eyes, and saw, and, behold, there stood before the river a ram which had two horns: and the two horns were high; but one was higher than the other, and the higher came up last.

Dan. 8:20 The ram which thou saw, that had the two horns, they are the kings of Media and Persia.

Goat

Notable Horn

Daniel equates the notable horn of the goat with the first king of the Greek Empire: Alexander the Great.

Dan. 8:5 And as I was considering, behold, a he-goat came from the west over the face of the whole earth, and touched not the ground: and the goat had a notable horn between his eyes.

Dan. 8:21 And the rough he-goat is the king of Greece: and the great horn that is between his eyes is the first king.

Four Horns

Daniel equates the four horns of the goat with the four kingdoms of the Greek Empire into which the Greek Empire was divided after the death of Alexander the Great.

Dan. 8:8 And the he-goat magnified himself exceedingly: and when he was strong, the great horn was broken; and instead of it there came up four notable [horns] toward the four winds of heaven.

Dan. 8:21-22 And the rough he-goat is the king of Greece: and the great horn that is between his eyes is the first king. And as for that which was broken, in the place whereof four [horns] stood up, four kingdoms shall stand up out of the nation, but not with his power.

Ten Horns

Daniel and Revelation equate the 10 horns of the beast with 10 kings.

Dan. 7:7 After this I saw in the night-visions, and, behold, a fourth beast, terrible and powerful, and strong exceedingly; and it had great iron teeth; it devoured and brake in pieces, and stamped the residue with its feet: and it was diverse from all the beasts that were before it; and it had 10 horns.

Dan. 7:23-24 Thus he said, The fourth beast shall be a fourth kingdom upon earth, which shall be diverse from all the kingdoms, and shall devour the whole earth, and shall tread it down, and break it in pieces. And as for the 10 horns, out of this kingdom shall 10 kings arise: and another shall arise after them; and he shall be diverse from the former, and he shall put down three kings.

Rev. 17:3 And he carried me away in the Spirit into a wilderness: and I saw a woman sitting upon a scarlet-colored beast, full of names of blasphemy, having seven heads and 10 horns.

Rev. 17:12 And the 10 horns that thou saw are 10 kings, who have received no kingdom as yet; but they receive authority as kings for one time period with the beast.