Historically trellis was used as a framework to grow an assortment of vines and flowering climbers on. The word trellis derives from the French word treillage, meaning a latticework for supporting vines.
These days trellis is used in a number of different ways, e.g. to provide screening or a windbreak, to divide an area, as well as other structural and visual functions within a garden. 
With modern gardens, ever diminishing in size, the trellis becomes a firm favourite for growing cucumbers, peas, beans,
tomatoes and aubergines and getting these vegetables off the ground will produce a better crop; it also protects them from insects that are in the soil. Having the fruits above ground also prevents them from rotting, by not resting on poorly drained or wet soil.
In addition, of course, the ever popular use of trellis with an arbour and, or gate to give a welcome to visitors or, consider how trellis can bring further dimension to your garden. 
