A bulkhead is a structure that can separate a pool into different sections. Typically these structures are moveable in the United States to allow the pool to be adjusted to accommodate different field of play (Yards and Meters). For example, in a 50 meter pool with 2 movable bulkheads there can be as many as 19 different course configurations that can support swimming, water polo and synchronized swimming. For NCAA swimming, race courses that utilize a bulkhead as a turning surface must be Certified for each session of a competition. Courses with two hard walls require certification only once. In the United States movable bulkheads are typically 4 or 6 feet wide. 
Bulkheads that are designed to move typically rest on the pool gutter. There are either skid plates or wheels on the bottom of the bulkhead that role along the pool gutter lip. 
Many of the bulkheads that are designed to move have the ability to be filled with air to minimize the weight impact when moving the structure. Some are completely buoyant. Other manufactures provide a power driven solution. When the bulkhead reaches its new position it is secured in place with a mechanism to confirm the proper dimension for the activity. If air was used to move the bulkhead it would be removed to add stability to the structure during programming.
Switching a pool between long course and short course can be very time consuming. Nonetheless some facilities switch back and forth daily. In the United States where 25 yard courses are important many 50 meter pool have a 25 yard with. This allows switching from 50 meters to 25 yards without relocating bulkhead(s). Most world markets only swim in a metric format. In these situations a retractable bulkhead can be used that recesses into the floor. This allows for the pool to be shorter since the width of the bulkhead does not need to be taken into account in the 50 meter dimension. This is the solution that is uses at the London Olympic Facility.
Alternatively, some bulkhead manufacturers can provide passages through bulkhead for the 50 meter lane lines. With this approach the pool can go from long course to short course without moving lane lines.
Bulkheads are typically made out of fiberglass or stainless steel. Issues that may impact material selection may include ability to easily move the bulkhead (weight), durability and maintenance requirements.
For competition swimming the end of the pool (or bulkhead) must be rigid enough and wide enough to accommodate officials, lap counters, etc. 
But, for training all you really need is a rigid turning surface. For this reason a submersible swim wall could be considered. This approach is very popular in Australia and the benefits are obvious. First of all the pool can go from long course to short course very quickly by simply raising the swim wall from its resting place on the pool floor. Air is added to the swim wall to raise it and released to lower it. Another benefit is that swim walls are typically the width of two lanes and can be raised individually in about 1 minute. This allows a single 50 meter pool to offer short course and long course swimming at the same time! Some pools in Australia have traditional bulkhead for competition and swim walls for daily training.
An economical version of a movable swim wall is basically a turning wall that simply attaches to the floating lane lines. They are very affordable, surprisingly stable and easy to install/remove.
Thank you for use of the above photos from Stark Industries, Vario Pool, Anti Wave International, Finis USA, Neptune Benson