The Western Red cedar tree is what most people (at least in the Northwestern United States) refer to when they use the term "cedar". It is commonly used for fences and exterior siding because it can get wet without rotting.
It leaves and wood have a fairly strong and distinct aroma. This may be the source of the name "cedar" as this aroma is similar to the aroma of the true cedars (ie. Cedar of Lebanon).
I took the images in this post while on a recent trip to Washington state and Vancouver BC. The images above are from Berthusen Memorial Park in Lynden, Washington. The images of the two trees below are from Stanley park in Vancouver. I spent about four hours walking the trails of the park and observing the very large Western Red Cedars that can be seen throughout the park.
Due to a recent storm there were a great many trees that had been blown down and were being gradually removed park service crews. It was a pity to see even some of the very old giants lying on the ground. Another interesting sight in the park are the "nurse logs". These are logs or stumps that have decomposed and have smaller trees growing on top of them and benefiting from their nourishment.
The BIG stump in the picture below is found at a rest area along Interstate 5 north of Seattle but south of Arlington. It is all that remains of a giant Western Red Cedar that grew in the area before it was killed by a fire in 1893. The stump of this tree is 20 feet across at the base.