Bulkheads are usually found on waterfront property. They are that wall you see where the land meets the water and are used to keep the soil from being washed away.
Bulkheads can be constructed from wood, metal, stone or concrete and usually consists of piles being driven into the ground with a wall then attached to the piles. Soil is then placed against the bulkhead on the land side. A bulkhead that has failed can allow the adjacent water to then erode away the soil and eventually cause the adjacent house or building to collapse.
As a bulkhead is in water it should be inspected by a professional to insure that it is sound.