* Synchronous Digital Hierarchy: This is the most common meaning of SDH, referring to a standard for multiplexing digital signals in telecommunications.
* Sustainable Development Hub: This is used in the context of sustainable development initiatives.
* Software Defined Hardware: This refers to a type of hardware that is controlled and configured by software.
* Standard Deviation of the Histogram: This term is used in statistical analysis.
* Southern District of Houston: This refers to a specific geographical location in the United States.
To know the correct full form of SDH, you need more context. What is the topic or situation you are referring to?