Well I;m glad this isn't one of my exam questions, I have no clue what 'base dressing' could mean... but then I probably haven't done the course you're doing.

I had to look it up, myself, Bamboo. They never called it that in my Master Gardener classes, back in the Dark Ages.
Base dressing is when you work nutrients into the soil before planting plants or sowing seeds. I have found it to be most useful in applying slow acting natural fertilizers, such as bone meal, hoof, horn, and hide meal, K-Mag, or volcanic ash. With base dressing, the nutrients are already available in the root zone as the plant grows, so the plants spend less time playing "catch up" when you realize that there is a deficiency. Caution is indicated, since if too much is applied, it is difficult to do anything about it, for the next year or two.
Top dressing is used with more or less soluble solid fertilizers. Over time, the nutrients leach out of the fertilizer, and travel down to the root zone. Some fertilizers leach in quickly, such as ammonium sulfate, while others, such as timed release formulas, are much slower. With top dressing, deep watering is indicated after application, since natural rainfall may not be enough to prevent fertilizer burn. Occasionally, the slower forms will wash away in heavy rainfall, before they have time to do their job. Here in the desert, they sometimes blow away! :)
There are two forms of liquid fertilizing: soil application, and foliar application. With soil application, it works the same as top dressing, but usually much more quickly--sometimes too quickly! Since the nutrients are already in soluble form, they can leach out of the root zone very quickly, also, so frequent applications may be necessary. Foliar applications involve spraying highly diluted solutions of nutrients directly on the leaves. That is a good way to apply nutrients that are quickly bound by the soil, such as phosphate and micronutrients in the alkaline soil where I live, and when you need instant results. Frequent applications are usually indicated. Caution here too, because if the solution is too strong, the plants can burn severely.
I hope this helps, Msorganic.

So base dressing is what I do when I prepare an area for planting and incorporate composted manure and the like? I always call that soil emendment.... and its not clear they're talking about unplanted ground, though it did occur to me they might also mean organic mulch, although really that's topdressing. I already know the other two, it was just the term 'base dressing'...

From what I can see, "base dressing" applies mostly to fertilizers mixed into the soil, rather than the bulk organic material.