FIG. 1 is a top plan view of a retaining wall building block of a first embodiment showing my new design;

FIG. 2 is a right side elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a rear elevational view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a front view of a retaining wall building block of a second embodiment.