A true beginner swimmer is someone that isn't comfortable in the water, hasn't learned to float or tread water. Generally beginner classes teach comfort in the water, elementary backstroke, breaststroke and the front crawl. If you can tread water and swim 1 length, you aren't really considered a beginner.
Intermediate swimmers kind of run the gamut. At the low end of intermediate, you can swim 1-4 lengths in comfort, you know a couple strokes, and are somewhat comfortable in the water. As you get towards advanced intermediate, then you know all four strokes, you may be able to do flip turns, and can easily swim 200m and up. At the high end, you can do basically smaller versions of swim team workouts.
Once you get to the advanced level, you have complete comfort in the water, you can do all four strokes well, flip turns, maneuver underwater, things like this. Most swim team members will be in the advanced intermediate to advanced level. At this level you are also working on small, subtle stroke refinements in order to increase your speed in the water.
So if you can swim a few laps comfortably and have at least a familiarity with breaststroke/backstroke, then you fall somewhere in the intermediate segment.