There is much confusion about this concept nowadays. There needn’t be. Scripture is clear:

“And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved.” Acts 4:12 English Standard Version (ESV)

Calvin says:

Neither is there salvation in any other. …And assuredly Christ had showed this one token of his grace, to the end [that] he might be known to be the only author of life. We must consider this in all the benefits of God, to wit, that he is the fountain of salvation. And he meant to prick and sting the priests with this sentence, when as he says that there is salvation in none other save only in Christ, whom they went about to put quite out of remembrance.

As if he should say, that they are twice damned who did not only refuse the salvation offered them by God, but endeavor to bring the same to naught, and did take from all the people the fruit and use thereof. Although he seems to speak unto deaf men, yet he preaches of the grace of Christ, if [perhaps] some can abide to hear; [and] if not, that they may at least be deprived of all excuse by this testimony.

Neither is there any other name…Salvation (says he) is in Christ alone, because God has decreed that it should be so. For by name he means the cause or means, as if he should have said, forasmuch as salvation is in God’s power only, he will not have the same to be common to us by any other means than if we ask it of Christ alone.

Whereas he says under heaven…I do rather think that this was added, because men cannot ascend into heaven, that they may come unto God. Therefore, seeing we are so far from the kingdom of God, it is needful that God does not only invite us unto himself, but that reaching out his hand he offer salvation unto us, that we may enjoy the same.

Peter teaches in this [passage], that he has done that in Christ, because he came down into the earth for this cause, that he might bring salvation with him. Neither is that contrary to this doctrine, that Christ is ascended above all heavens, (Ephesians 4:10). For he took upon him our flesh once for this cause, that he might be a continual pledge of our adoption. He has reconciled the Father to us forever by the sacrifice of his death: by his resurrection he has purchased for us eternal life.

And he is present with us now also, that he may make us partakers of the fruit of eternal redemption; but the revealing of salvation is handled in this [passage], and we know that the same was so revealed in Christ, that we need not any longer to say, “Who shall ascend into heaven?” (Romans 10:6).

And if this doctrine were deeply imprinted in the minds of all men, then should so many controversies concerning the causes of salvation be soon at an end, wherewith the Church is so much troubled…

The Visual Bible – Acts Chapter 4