Aside from the original 12 Apostles, an Apostle is also a Ministry gift of the Church as a missionary or other special responsibilities.
General references to Apostles:
Now there were in the church that was at Antioch certain prophets and teachers; as Barnabas, and Simeon that was called Niger, and Lucius of Cyrene, and Manaen, which had been brought up with Herod the tetrarch, and Saul.
2 As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them.
3 And when they had fasted and prayed, and laid their hands on them, they sent them away. (Act 13:1-3 KJV)Learn More