stray
To wander away from where you are supposed to be.
Stray means to wander away from where you're supposed to be or to drift off course. A dog that strays from its yard might end up several blocks away, following interesting smells. During a class discussion, your thoughts might stray from the lesson to what you're having for lunch.
When something or someone strays, they've left the intended path, whether that's a physical route, a planned topic, or expected behavior. A hiker who strays from the marked trail could get lost in the woods. In an essay, if your paragraphs start to stray from your main point, your teacher might write “stay focused” in the margins.
As a noun, a stray is an animal, usually a dog or cat, that has wandered away from home or doesn't have one. Stray animals often look for food and shelter on their own. Animal shelters take in strays, hoping to find them homes.
The word carries a sense of unintentional wandering rather than deliberate choice. You might purposely take a different route home, but when you stray, you've drifted without really meaning to. A baseball that strays outside the strike zone becomes a ball rather than a strike.