Concise Bible Dictionary:

A term used in the O. T. for Israel as sheep gathered by God as their Shepherd, and called Jehovah's flock (Psa. 77:2020Thou leddest thy people like a flock by the hand of Moses and Aaron. (Psalm 77:20); Psa. 107:4141Yet setteth he the poor on high from affliction, and maketh him families like a flock. (Psalm 107:41); Jer. 13:1717But if ye will not hear it, my soul shall weep in secret places for your pride; and mine eye shall weep sore, and run down with tears, because the Lord's flock is carried away captive. (Jeremiah 13:17)). It is also applied to those of Israel that were gathered to Christ when on earth. To these He added the Gentile believers; and all were united into one flock (not “one fold”), with Christ as the one Shepherd (John 10:1616And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd. (John 10:16)). When the leaders of Israel were to be judged as not caring for the Lord's flock, the prophet speaks of the remnant as the poor of the flock (Zech. 11:7, 117And I will feed the flock of slaughter, even you, O poor of the flock. And I took unto me two staves; the one I called Beauty, and the other I called Bands; and I fed the flock. (Zechariah 11:7)
11And it was broken in that day: and so the poor of the flock that waited upon me knew that it was the word of the Lord. (Zechariah 11:11)
: Compare Luke 6:2020And he lifted up his eyes on his disciples, and said, Blessed be ye poor: for yours is the kingdom of God. (Luke 6:20)). The Lord also spoke to His disciples as a little flock, bidding them not to fear: it was their Father's good pleasure to give them the kingdom (Luke 12:3232Fear not, little flock; for it is your Father's good pleasure to give you the kingdom. (Luke 12:32)). In Paul's address to the elders of Ephesus he exhorts them to take heed unto all the flock: the wolves would not spare them. Paul commended the shepherds to God and to the word of His grace (Acts 20:28-2928Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood. 29For I know this, that after my departing shall grievous wolves enter in among you, not sparing the flock. (Acts 20:28‑29): Compare 1 Pet. 5:2-32Feed the flock of God which is among you, taking the oversight thereof, not by constraint, but willingly; not for filthy lucre, but of a ready mind; 3Neither as being lords over God's heritage, but being ensamples to the flock. (1 Peter 5:2‑3)).