A mirror is a type of lens and all lenses have a so called *focus point* or *focal point.* This just means that all the light that passes through the lens or is reflected by it will be redirected to a specific point. You can think of it like a multi-lane highway which narrows to just a single lane, all the cars will be redirected to the single lane (the focus point).
Now, mirrors are usually designed with the focus point in mind. The designer of the mirror might have designed it so that you are supposed to stand a certain distance from it. This means that they will design the focus point to focus to reflection to that distance so you will have a sharp image. The effect of this is also that things further away or closer to the mirror might appear distorted or blurry.
The placement of the focal point will have a big impact of what type of lens you have and it’s properties. For example it will dictate if the lens is convex or concave, meaning it will magnify or shrink the thing you are looking at. You can also create weird effects by having multiple focus points which can result in funny reflections like the ones you can find in a house of mirrors at a theme park.
Edit:
As pointed out by u/Mand125 my explanation is not applicable for flat mirrors, which probably are the most common mirrors and presumably what OP is asking about.
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