A Sign Language Interpreter is a person who converts spoken language into a signed language for the deaf
or hard of hearing
There are various signed languages throughout the world. Even in America several variations are used.
SEE - Signed Exact English is a straight word for word translation of English. This form uses a sign for each spoken English word. Not very common.
ASL - American Sign Language is the most common language used by the deaf. This form has its own grammar and sentence structure. English is translated into ASL word order using signs.
There are also many combinations of these two forms of sign. The variation an interpreter would use depends on the preference of the deaf or hard of hearing person.
Sign Language Interpreters are also expected to follow a Code of Ethics. This Code may vary slightly from state to state but is overall very similar.