The notation gamma of G, represented as γ_n(G), refers to the n-th term of the lower central series of a group G. It serves as a descriptive notation similar to sequences in mathematics, where each term is defined by a specific operation. The lower central series is unique to each group, allowing the gamma notation to act as an operator that maps the group to its corresponding term in the series. This notation helps in understanding the structure and properties of the group through its lower central series. Overall, gamma of G is a crucial concept in group theory for analyzing group behavior.