Those of us wearing glasses know too well what blurry, out of focus, and un-sharp looks and feels like. We experience it every day when we take off our glasses. If your vision is perfect, try borrowing a pair of strong glasses and you will immediately know what blurry is. Lines and edges turn soft so seeing details and reading become very difficult or impossible.
This is my original shot. As sharp as my phone could make it.
Blurry level 1. Notice the softer edges around leaves and letters. What other details are blurred?
Blurry level 2. My eyes try to compensate to make the text sharper. To no avail. Leaves started merging into each other.
Blurry level 3. You can still read the sign, but only because the letters are huge. Individual leaves are gone and some details of the fence have dissolved.
Motion blur. This is a slightly different kind of blurring. The sign would look like this if shot from a moving bicycle or car.
Hold your breath or use some support when shooting.
Give your camera time to focus.
Avoid taking pictures in low light.
Get a better camera phone if possible.
If you suspect your shot is blurry, it probably is! Zooming in will let you know. Please delete it and take a better pic. Be critical and don't upload blurry pics.
Since photos on Google Maps are mostly shown as a small image you can choose to improve the sharpness by using photo editing software. Also, reducing the size can make images look sharper. But proper sharpness is always better.
You can find many blurry photos uploaded to Google Maps. I tend to flag such photos as Poor quality as a small contribution to improving Google Maps. You could do the same.
Find Google's official statements about this issue in the Photo Rules. Scroll down and open 13: Always super sharp. This issue is also addressed in What photos should I share on Google Maps? by Google Moderator MoniV.
Hit "Suggested next page" to see why too dark images should not be uploaded to Google Maps.