Beta-decay can be a little tricky. It is the ejection of a fast-moving electron - a beta particle - from the nucleus of an unstable nuclide.
Figure 1: Beta decay process.
When a daughter nuclide is produced via beta decay the effect is to raise the nuclide's atomic number by one, while leaving the mass number unchanged.
Beta emitters are super useful too! We use them in medicine to map out and produce images from inside the human body. They can be swallowed as a liquid solution or injected directly into the bloodstream. As they travel around the body they emit beta particles which can be detected by very sensitive instruments like positron emission tomography (PET) scanners.