The act of petitioning God or praying on behalf of another person or group. The sinful nature of this world separates human beings from God. It has always been necessary, therefore, for righteous individuals to  go before God to seek reconciliation between Him and His fallen creation.
     One of the earliest and best examples of intercession of this type occurs in Genesis 18, where Abraham speaks to God on behalf of Sodom. His plea is compassionate; it is concerned with the well-being of others rather than with his own needs.
     Stephen’s death is another remarkable example of a Godly man interceding for his enemies. Acts 7:59-60 - And they stoned Stephen, calling upon God, and saying, Lord Jesus, receive my spirit. And he kneeled down, and cried with a loud voice, Lord, lay not this sin to their charge. And when he had said this, he fell asleep. (What a testimony)
     Christ is , of course, the greatest intercessor of all. He made intercession with the Father for all mankind. Is. 53:12 - Therefore will I divide him a portion with the great, and he shall divide the spoil with the strong; because He hath poured out His soul unto death; and He was numbered with the transgressors; and He bare the sin of many and made intercession for the transgressors.
     Christ petitioned God on behalf of those who crucified Him. Luke 23:34 - Then said Jesus, Father forgive them for they know not what they do. And they parted His raiment, and cast lots.
     Our acceptance by God depends upon Him. Ro. 8:34 -  Who is He that condemneth? It is Christ that died,  yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us.
     Our salvation is through Christ’s intercession. He. 7:25 - Wherefore He is able to save them to the uttermost that come unto God by Him, seeing He ever liveth to make intercession for them.
     The Holy Spirit intercedes on behalf of individual Christians. Ro. 8:26-27 - Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered. And he that searcheth the hearts knoweth what is the mind of the Spirit because he maketh intercession for the saints according to the will of God.
There should be no reason for us to not know how or what to pray. What Divine Help is available to us.
     Finally, we as Christians are urged to intercede for all people. I Tim. 2:1 - I exhort therefore, that, first of all, supplications, prayers, intercessions, and giving of thanks be made for all men; vs-2- For kings, and for all that are in authority; that we may lead a quiet and peaceable life in all godliness and honesty.( Pray for our leaders and all people in authority)

Key - Our attitude should be compassionate, having a concern for others needs rather than our own.
            Such selfless concern is the mark of all true intercession.