These names are unofficial.
B: Any glider that resembles a B, a B descendant, or evolves from the B-heptomino.
Calcyman goes fishing: This 31-cell still life. The name comes from a wonderful post by user Saka
Dot: The one-cell still life in B/S0
G: The basic glider in any rule. (e.g. The p2 c/2 in Snowflakes, glider in Life)
R: Any glider that resembles an R, an R descendant, or evolves from the R-pentomino.
X: A 5-cell still life, minimal rule B/S1c4c
Y: A 5-cell still life, minimal rule B/S1c2ae4y
Z: A 5-cell still life, minimal rule B/S2ae4z