In Parallel
Going Abreast, Concurrent
noun, verbal noun, の adjective
If several people were to line up and go together, they'd all be advancing in parallel while going abreast of one another.
While 平行 simply refers to things being parallel geometrically, 並行 is used for two or more things placed or moving alongside 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 — things which are concurrent, in other words.
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.
This also runs in parallel with 平行 when it comes to its reading, so that can make it easier to remember too.
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 and the bicycle travel alongside each other through the stretch where the train tracks and the road run side by side.
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.