Is this dust or dead pixel?

qrk

It's a dust speck on your sensor. Using a smaller aperture (higher f-stop number) will make it more apparent. This is a common thing. You can try blowing the dust speck off using a rocket blower. Or wet-swab the sensor. Wet swabbing the sensor can get you in more trouble if you aren't well practiced. The safest thing to do is ignore it or take your camera to a shop where they can do it for you. You will get more dust bunnies on your sensor as time goes on.

Frank

Definitely NOT dead pixels, but instead just common dust. Pixels are electronically wired like Christmas tree lights, so when one goes, the whole string is dead. If a pixel should die, you'd see an entire line of dead pixels and not just a fuzzy gray dot. Fuzzy dots is what dust on the sensor looks like.

keerok

Most probably dirt. Pray it isn't fungi. Try cleaning with lens cloth (the one from a camera store not the one with your eyeglasses) or lens paper (from a camera cleaning kit).