-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.
Bryan Pawlina's answer is pretty good. It gives a physical description of the Moment of Inertia (MoI) pretty well and provides a general idea on how to calculate it. A Moment is a mathematical term that is similar to vector products. It essentially is the integral (or summation) of a function * input to function.