Ordinary
Average
noun, の adjective
The things that line up are ordinary and average things. Because the majority of things (or people) fall into the average category, you could say most of them line up side by side with each other.
This might be why 並 is often used in restaurants to refer to standard (or average) portion sizes. And in sushi restaurants, 並 can refer to a standard set, as opposed to a more luxurious or premium one.
Note that when describing something as 並 outside of a restaurant or commercial context, it could have a slightly judgmental tone. Most people wouldn't love it if you called their work (or them) ordinary and average, you know?
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you to remember:
You're at the coast, looking out at the 波 (なみ), which are all very ordinary, average. Nothing exceptional about those waves.
この巻きずしセット、並と上があるんだけど、どっちがいい？
We have an ordinary and a luxury makizushi set. Which one would you like?
並の努力では、ここまで成功することはできないよ。
You can't achieve this level of success with just ordinary effort.
運動神経は並だったが、頭はすこぶる良かった。
He had average reflexes, but a great mind.