Electron capture is a decay mode for chemical elements that will occur when there are too many protons in the nucleus of an atom, and there isn't enough energy to emit a positron.
In this case, one of the orbital electrons is captured by a proton in the nucleus, forming a neutron and a neutrino. Since the proton is essentially changed to a neutron, the number of neutrons increases by 1, the number of protons decreases by 1, and the atomic mass remains unchanged. By changing the number of protons, electron capture transforms the nuclide into a new element.