The word apostle means sent one.
Apostles in scripture were those sent by the Lord Jesus Christ to preach the gospel, make disciples of nations, cast out devils, perform miracles etc.
There are 12 apostles of the lamb who will sit on thrones, and there are Ephesians 4:11 apostles that the Lord sends for the full duration of the Church age until we come to full measure and stature of Christ.
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Ephesians 4:11-16
11 And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers;
12 For the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ:
13 Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:
14 That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive;
15 But speaking the truth in love, may grow up into him in all things, which is the head, even Christ:
16 From whom the whole body fitly joined together and compacted by that which every joint supplieth, according to the effectual working in the measure of every part, maketh increase of the body unto the edifying of itself in love.