Okay, so Saleh is a name that some people have. It's like how your name might be Emily or Sam or Liam. Saleh is a name that is common in some parts of the world, like in Arab countries.
But Saleh can also mean something else. When we say "saleh" like a word instead of a name, it means "good" or "righteous" in Arabic. This is because in Islam, which is a religion followed by many people in Arab countries, there is a prophet named Saleh who was known for being a good and righteous leader. So when people say "saleh" to mean "good" or "righteous," they are honoring that prophet and his teachings.
So if someone says "That was a saleh thing to do," they mean that it was a good and righteous thing to do. It's like they're saying "You did something really awesome and we should all be proud of you."
Does that make sense, kiddo?