Definition: Interplanting is the practice of planting a fast-growing crop between a slower-growing one in order to make the most of your garden space. An example of this would be sowing lettuce seeds between broccoli plants; the lettuce will grow happily in the space and shade provided by the broccoli plants, and you will be able to harvest it before the broccoli is large enough to totally shade it out.
Also Known As: Intercropping
Alternate Spellings: Inter planting
One method of interplanting I like to use is to sow mesclun seeds around my tomato seedlings, so that I can harvest salad greens while waiting for my tomato plants to start producing.