The term, "plan of salvation" is used to refer to a few different ideas.
First, we have the general idea that we die and sin, and, as such, we lack the immortality and purity that is characteristic of God, our father, and these create a barrier we cannot overcome both to returning to be with him, as well as to be like him. The Plan of Salvation is the overall idea, that a savior, Jesus Christ, was provided for us to overcome these obstacles, by overcoming death so that we could all be resurrected, and by taking our sins him, providing us a method to clean ourselves of our sins by exercising faith in him. (Exercising faith, being a term which encompasses, generically, believing in him in a manner that motivates us to follow him, and do what he asks of us. Thus it covers repentance, obedience to commandments, and doing anything else he might teach us to help us become like him.)
Second, we have a kind of lifecycle of an intelligence, or lifecycle of a spirit. It should be obvious that this is related to the first meaning of the plan of salvation.
Third, we see this term applied to the process we go through during our lives to qualify for salvation. This is a sort of ideal process described for people who live to be able to choose to take each step. This is also related to the first definition of the Plan of Salvation.