What is baptism?
The cleansing ritual which means acceptance by Christ into heaven. Different religions baptise at different age levels. You can be baptized at most any age, infant to adult.
Some Christians see baptism as a means of salvation, and others see it as a sign of a foregoing act of trusting in Christ which can only be from a person of an age to speak for themselves. Infant baptism involves a belief that others can speak on behalf of the child. Either way, it is signifies the new life and washing away of the old nature.
Scripture says that Jesus instructed His disciples to "Go therefore and make disciples of all nations, baptising them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you; and lo, I am with you always, to the close of the age."(Matthew Ch 28)
What is Baptism: "Now there was a man of the Pharisees, named Nicodemus, a ruler of the Jews. This man came to Jesus by night and said to him, 'Rabbi, we know that you are a teacher come from God; for no one can do these signs that you do, unless God is with him.' Jesus answered him, 'Truly, truly, I say to you, unless one is born anew, he cannot see the kingdom of God.' Nicodemus said to him, 'How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?' Jesus answered, 'Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. Do not marvel that I said to you, 'You must be born anew.' The wind blows where it wills, and you hear the sound of it, but you do not know whence it comes or whither it goes; so it is with every one who is born of the Spirit.' Nicodemus said to him, 'How can this be?' Jesus answered him, 'Are you a teacher of Israel, and yet you do not understand this? Truly, truly, I say to you, we speak of what we know, and bear witness to what we have seen; but you do not receive our testimony. If I have told you earthly things and you do not believe, how can you believe if I tell you heavenly things? No one has ascended into heaven but he who descended from heaven, the Son of man. And as Moses lifted up the serpent in the wilderness, so must the Son of man be lifted up, that whoever believes in him may have eternal life.'" (John Ch3)
According to Scripture therefore Baptism enables us to enter the Kingdom of Heaven through our spiritual birth.
Entry to the Kingdom of Heaven in this way cannot be denied as we see when John the Baptist "saw many of the Pharisees and Sadducees coming for baptism, he said to them, "You brood vipers! Who warned you to flee from the wrath to come? Bear fruit that befits repentance." (Matthew Ch 3) and when Jesus said "Truly, I say to you, among those born of women there has risen no one greater than John the Baptist; yet he who is least in the kingdom of heaven is greater than he. From the days of John the Baptist until now the kingdom of heaven has suffered violence, and men of violence take it by force "(Matthew Ch 11)
There are other ways to enter the Kingdom of Heaven e.g. 'Let the children come to me, do not hinder them; for to such belongs the kingdom of God. Truly, I say to you, whoever does not receive the kingdom of God like a child shall not enter it.'." (Mark 10). "Not everyone who says to me 'Lord, Lord' shall enter the kingdom of heaven, but he who does the will of my Father who is in heaven" (Matthew Ch 7) "Blessed are those who are persecuted for righteousness' sake, for theirs is the kingdom of heaven. ….." (Matthew Ch 5)
Note 1: Jesus was baptised by John "for thus it is fitting for us to fulfil all righteousness. ..... And when Jesus was baptised, he went up immediately from the water, and behold, the heavens were opened and he saw the Spirit of God descending like a dove, and alighting on him; and lo, a voice from heaven, saying, 'This is my beloved Son, with whom I am well pleased.'" (Matthew Ch 3) thus confirming His entry into the Kingdom of Heaven and His sonship of the King of Kings.
Baptism is when someone very young or newborn is being parted from their sins.
A ceremony or occasion at which this takes place. This is the definition in the dictionary.