What is a graduate research assistantship? What is the actual meaning of being a research assistant? I have only heard of masters in science and PhD.
A graduate research assistant—regardless of field–is someone who is carrying out research, normally as part of studies that will ultimately lead to either a master's or a PhD (or degree of some other kind). In general, a "graduate research assistant" (or other similar terms) are administrative in origin—it's the name for the "job" that graduate students have while they progress toward their degrees.