In Parallel
Going Abreast
noun, verbal noun, の adjective
Line up and go together. If you did that, you'd be in parallel or going abreast with someone.
並行 refers to two or more things placed or moving parallel to each other, like buses or trains running side by side. It's also used to describe two or more activities happening at the same time.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
私、並行して何かをするのは苦手なんです。
I'm not good at doing things in parallel.
今、二つの小説を同時並行で書いています。
I am currently writing two novels at the same time.
線路と道路が並行している区間を、電車と自転車が並行して走るシーンが好きなんです。
I like the scene where the train runs parallel with the bicycle, along a section of track that's side by side with the road.
複数の言語を並行して勉強することは、ひとつだけを学習するよりも効率的だと聞いたことがあります。
I heard that studying multiple languages at the same time is more efficient than only studying one.