Final answer:
A reaction involving the gain of one or more electrons is known as a reduction reaction, which is a part of redox reactions where oxidation and reduction occur simultaneously.
Step-by-step explanation:
A reaction involving the gain of one or more electrons is a reduction reaction. This process is part of oxidation-reduction (or redox) reactions, which are chemical reactions that involve the transfer of electrons. One easy way to remember this concept is the mnemonic OIL RIG, which stands for "Oxidation Is Loss, Reduction Is Gain" of electrons. In chemical reactions, the substance that gains electrons through reduction is said to be reduced, and this process can also be associated with the loss of oxygen or the gain of hydrogen in molecular compounds. The key takeaway is that in redox reactions, oxidation and reduction always occur together, meaning while one substance is oxidized by losing electrons, another substance is reduced by gaining electrons.