The swim, bike, and run. Brick is a key tool in training for a triathlon. It can be done at many different durations and intensities.
Bricks can be modified to bike and run. Just because of time and logistics. So, a swim can be done the night before a long bike and run brick workout. I have even prescribed swim, run, swim, run bricks. Another one I like is to alternate is run, bike, run, bike, run that is one that works well indoors or at a track with a bike trainer. The Brick can be done long and easy in the base portion of the training, just to get your body used to riding and running long. I also believe in performance based training in the build several weeks out from race day. I like to find bike intensity that can be held for the length of the race and being able to run effectively.
I even consider a transition run of a mile or two, a brick workout. Another form of a brick is just go do a race. Find a local event and turn it into a training day. Getting out with like-minded people, supporting a local race and working on your endurance all at the same time!