I have a blister on the bottom back of my foot and in the middle of this blister is like a white spot , what does this mean?

Good question..: How did you get the blister? how long has it been there? Any pain at all? If it gets worse or more painful, see a Podiatrist for a full evaluation.

Hard to say: blisters are usually caused by friction, such as wearing loose shoes with no socks. it could also be an infection like athletes foot or a bacterial abscess. other potential causes include a thermal burn, contact allergic reaction or the beginning of a systemic blistering skin condition. without seeing you and obtaining history, it is impossible to tell. see a podiatrist ASAP. 5619950229