A nuclear reaction given by $_{Z}X^{A} \rightarrow\ _{Z+1}Y^{A} +\ _{-1}e^{0} + \bar{\nu}$ represents

In this reaction, the mass number A stays the same and the atomic number increases by 1.
An electron ($_{-1}e^0$) and an antineutrino ($\bar{\nu}$) are emitted.
This happens when a neutron in the nucleus changes into a proton: $n \rightarrow p + e^- + \bar{\nu}$.
Emission of an electron and an antineutrino with no change in mass number is $\beta^-$-decay.
($\gamma$-decay changes neither A nor Z; fusion and fission change the nuclei involved completely.)