-blast. A suffix meaning an immature precursor cell of the type indicated by the preceding word. [G. blastos, germ]. immature precursor cell type; the cell type is denoted by the preceding syllables, e.g. osteoblast.
(plural defining moments) A moment in time that defines something, such as a person's success or failure, achievement or demise, talent, etc. A point at which the essential nature or character of a person, group, etc., is revealed or identified.
I think Wikipedia's definition is actually pretty clear: In physics, moment is a combination of a physical quantity and a distance. Notable examples: The moment of force (torque) about a given axis is given by the force (physical quantity) times the perpendicular distance of the line of action from the axis.