The phrase "parallel passage" means two or more sections of a text that are similar or comparable to each other. It could be referring to sentences, paragraphs, or even entire chapters that have similar ideas or themes. Full definition
When Ephesians 5:18 - 20 is compared with the exactly parallel passage in Colossians 3:16, it becomes clear that being filled with the Spirit is exactly the same thing as letting Christ's Words dwell in you richly. (redeeminggod.com)
This passage parallels the passage in Romans chapter 8:17 And if children, then heirs; heirs of God, and joint - heirs with Christ; if so be that we suffer with him, that we may be also glorified together. (redeeminggod.com)
In the Synoptic Gospels Jesus is said to have spoken of the Son of Man no fewer than 69 times [38 times when parallel passages are disregarded], but the evangelists themselves make no use of the term. (religion-online.org)