Public Order
Public Safety, Public Peace
noun
If you rule so that your people can relax, then there will be good public order. You don't want the people you rule being upset or stressed out, you want public safety and public peace for all!
治安 refers to the overall state of security of a place, especially in terms of crime and social stability. You'll hear it in phrases like 治安がいい (the area is safe) or 治安が悪い (the area has poor public safety), usually in reference to particular cities or neighborhoods.
This is a jukugo word that uses on'yomi readings of the kanji. 治 has a couple of on'yomi readings though, so here's a mnemonic to help you remember 治安 uses the ち reading:
In order to promote public order, you put cheese (ち) on every street corner. The smell of cheese drives delinquents and criminals away. Or maybe free cheese just makes everyone so happy that they stop committing crime? Either way, the best way to ensure public safety is cheese.
この辺りは治安も悪くないけど、あの辺りは治安が良くないからね。
This area doesn’t have bad public safety, but that area does.
このまま日本の少子化が進むと、治安も悪化するでしょう。
If Japan's birthrate continues to decline, public safety will worsen.
俺は実はスーパーマンなんだ。この辺りの治安を守っているのはこの俺様なんだぜ。
I'm actually Superman and I'm the one who keeps the peace around here.