A painful swelling on the skin that contains liquid, caused usually by continuous rubbing, especially on your foot, or by burning. (Cambridge Dictionary)
A hollow rounded swelling that appears on a surface. (Cambridge Dictionary)
A blister is a painful swelling on the surface of your skin. Blisters contain a clear liquid and are usually caused by heat or by something repeatedly rubbing your skin. (Collins Dictionary)
Blisters: Pictures, Causes, Treatment, and Prevention – Healthline.
Blisters: Causes, treatments, and prevention – Medical News Today.