Parameters are effect variables.
usage type id [: semantic] [< annotation(s) >] [= expression];
Parameters can be read from and written to by the application with ID3DXEffect or ID3DXEffectCompiler.
Parameters can be referenced in functions and in techniques (specifically, in the right side of state assignments).
Parameters can be initialized to any valid HLSL Shader Reference expression that reduces to a literal value.
Parameter values are not changed by the execution of state assignment or function calls.