A sprinter is a person who regularly races distances of 50-100 yards/meters and does the race effectively, i.e. quick tempo, good breath control, quick reaction off the start, ability to six-beat kick on freestyle and backstroke with little effect on stroke rate. In workouts, a sprinter favors the short distance sets with lots of rest, or aerobic sets with enough recovery time. A sprinter might dabble in the 200s, but might be the one taking the race out very fast and getting caught at the end.
A middle distance swimmer will often swim 100-yard/meter races, but sticks primarily with the 200s, and will bump up to the 400 IM or 500 free on occasion. A middle distance swimmer tends to find a second wind or energy boost in the second half of a 200 race or exhibits more endurance at the end of 100 race than the sprinter, i.e. does not slow stroke rate or uses endurance boost to finish race. In workouts, middle distance swimmers favor VO2 max sets and will often do aerobic sets on a faster interval than sprinters, due to their higher endurance level. If you like doing 200s of the strokes, you belong here.
A distance swimmer will almost never be seen doing a race shorter than 200 yards/meters. He or she will always swim races longer than 200, and will call the 200 "a sprint." In workout, the distance swimmer wants sets to be have repeats longer than 200 with little rest. This swimmer loves the two-beat kick and will often do the 400 IM "for fun" because of the ability to effectively do the freestyle leg better than an IMer. Or do the 200 fly because it's not as bad as everyone talks about.
So, which one are you? You cannot be part of two groups at once. You might have started your swimming career as a sprinter then turned to distance, or vice versa. Or you could be a distance swimmer during the summer (for triathlons) and then go to middle distance in short course because the mile has too many turns.
I'm a sprinter. Duh. I haven't swum more than a 400 IM in a race since my teens.