"And I beheld, and I heard the voice of many angels round about the throne and the beasts and the elders: and the number of them was ten thousand times ten thousand, and thousands of thousands." (Revelation 5:11)
The number of God's holy angels is truly "innumerable" (Hebrews 12:22). John "beheld" so many angels at God's throne that he could not attempt to count them, but simply tried to express their immense multitudes by saying there were "myriads of myriads" and "chiliads of chiliads" (in New Testament Greek, a "chiliad" was the arithmetical term for "thousand" and "myriad" for "ten thousand," but both terms were often used to mean merely a great number).
The same Greek word occurs in Jude, verse 14: "Behold, the Lord cometh with ten thousands of his saints." These "holy ones" may also be angels, but it is even more likely (in view of 1 Thessalonians 3:13, Revelation 19:8-14, and other Scriptures) that these are redeemed men and women whose spirits had gone to be with Christ when they died in previous generations (Philippians 1:21-23; 2 Corinthians 5:8).
A parallel usage occurs in the Old Testament where the Hebrew word rbabah can mean either "ten thousand," specifically, or merely a very great number. It first occurs in God's great promise to Israel, conditioned upon their faithfulness to Him: "And five of you shall chase an hundred, and an hundred of you shall put ten thousand to flight" (Leviticus 26:8)--a promise more than literally fulfilled, for example, when Gideon's 300 men routed a Midianite army of 135,000 (Judges 7:6, 8:10).
But, whether speaking of the armies of faithful Israel, the redeemed of all the ages, or the great host of angels in heaven, the greatest superlatives must apply to Christ Himself, for He is "the chiefest among ten thousand. . . . he is altogether lovely" (Song of Solomon 5:10-16). HMM