Translation is the process of taking a document in one language and producing an accurate version of it in another language.
Sight Translation is the process of reading a document in one language and rendering a verbal equivalent in another language.
Interpretation is the process of verbally rendering an equivalent between languages. Interpretation can be either consecutive or simultaneous.
Consecutive means that one party speaks briefly and stops while the interpreter renders that part into the other language.
Simultaneous means that the interpreter (usually employing communications equipment) renders a near concurrent running verbal other language equivalent. Simultaneous interpretation is more demanding than consecutive and generally commands significantly higher cost. The performance demands of simultaneous interpretation are such that for lengthy sessions the interpreter needs to be spelled by another interpreter.