What is Repentance?

Repentance is a  change of mind  that results in a change of heart and direction.
It is a command given to all men and must be proclaimed in the name of Jesus for the forgiveness of sins.

Repentance is not turning over a new leaf or cleaning up your act.   It is not  doing more good things  than bad.   It is not  joining some religion and  conforming  to their rules and hoping when you die that all your good deeds will earn you Heaven.
One must first realize he cannot save himself nor merit a place in heaven.

God gives us the opportunity to repent, but we still decide to repent.  The evidence of true repentance is a changed life marked by good deeds and the fruit of the spirit.

It leads to salvation if there
is godly sorrow for sin
according to the will of God.

"For godly sorrow worketh
repentance to salvation not
to be repented of: but the
sorrow of the world worketh
death."  2 Cor 7:10

נָחַם nâcham, naw-kham'; a primitive root; properly, to sigh, i.e. breathe strongly; by implication, to be sorry, i.e. (in a favorable sense) to pity, console or (reflexively) rue; or (unfavorably) to avenge (oneself):—comfort (self), ease (one's self), 
a change of mind, as it appears to one who repents, of a purpose he has formed or of something he has done
1.To change one's mind.

2. To change one's mind for better, heartily to amend with abhorrence of one's past sins
There are different meanings of the same word in Greek language.  Also, in Hebrew language.
To care afterwards, i.e. regret
 What is the difference between worldly sorrow and godly sorrow?

Have you ever been sorry for just the consequences of sin, rather than the fact that the sin was evil in the sight of God?  I have.  That is worldly
sorrow.  Just feeling bad about sin does not mean it's godly sorrow.
When we have godly sorrow, we see our sin as God sees it: wicked and deserving of judgment.  We hate it and long for forgiveness from God.

Read Psalm 51 and see how King David wasted away with worldly sorrow
after committing adultery and with Bathsheba and murdering her husband.  After he was confronted with his sin, he came to a place of godly sorrow.  This earnest Psalm of repentance shows how David 
confessed his sin specifically and asked for deliverance from it.
He recognized  that nothing that he had or did could cover or pay for his sin, but all he had to offer God was brokenness over sin and the desire for change- he offered God his repentance.

Psalm 51 Audio Video                                                                          Repentance from Sin -  Laurence Justice

"Repent" definition Word-Study from the KJV Bible's Built-in Dictionary. Repentance, to repent, repent ye. King James Bible

2 Chronicles 7:14 - If my people, which are called by my name, shall humble themselves, and pray, and seek my face, and turn from their wicked ways; then will I hear from heaven, and will forgive their sin, and will heal their land.

1 John 1:9 - If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.

Acts 3:19 - Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord;

Luke 13:3 - I tell you, Nay: but, except ye repent, ye shall all likewise perish.

Ezekiel 18:21-23 - But if the wicked will turn from all his sins that he hath committed, and keep all my statutes, and do that which is lawful and right, he shall surely live, he shall not die.

Acts 17:30 - And the times of this ignorance God winked at; but now commandeth all men every where to repent:

2 Peter 3:9 - The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.

Proverbs 28:13 - He that covereth his sins shall not prosper: but whoso confesseth and forsaketh [them] shall have mercy.

James 4:8-10 - Draw nigh to God, and he will draw nigh to you. Cleanse your hands, ye sinners; and purify your hearts, ye double minded. 

Revelation 2:5 - Remember therefore from whence thou art fallen, and repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick out of his place, except thou repent.

Acts 2:38 - Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.

2 Corinthians 7:9-11 - Now I rejoice, not that ye were made sorry, but that ye sorrowed to repentance: for ye were made sorry after a godly manner, that ye might receive damage by us in nothing. 

2 Timothy 2:25 - 25 Flee also youthful lusts: but follow righteousness, faith, charity, peace, with them that call on the Lord out of a pure heart.

23 But foolish and unlearned questions avoid, knowing that they do gender strifes.

24 And the servant of the Lord must not strive; but be gentle unto all men, apt to teach, patient,

25 In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth;

Bible Verses About Repentance

Repentance in the Bible has three basic elements: a genuine sorrow towards God (II Cor. 7:9-10),

a genuine separation from sin (Heb. 6:1; Acts 26:20), and a genuine submission to God’s will (Acts 9:6; I Ths. 1:9). In other words, repentance involves a totally changed life. II Corinthians 5:17 says, “Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.” According to the Bible, all things are new once a man is in Christ, and old things are passed away. Repentance is certainly a requirement. Jesus began his ministry preaching, “Repent: for the kingdom of heaven is at hand.” (Mat. 4:17) In Matthew 9:13 he said, “. . . I am not come to call the righteous, but sinners to repentance.” He upbraided cities in Matthew 11:20 “because they repented not.” Repentance is required for salvation, and no honest and serious student of Scripture can claim otherwise.

The top photo is from my Websters 1828 Dictionary.. the watered 

down definition sure has changed over the centuries.