The ELIZA effect refers to the tendency of humans to attach associations to terms from prior experience. For example, there is nothing magic about the symbol "+" that makes it well-suited to indicate addition; it's just that people associate it with addition. Using "+" or "plus" to mean addition in a computer language is taking advantage of the ELIZA effect.
The ELIZA effect is a good thing when writing a programming language. For example, the operator overloading in many object-oriented programming languages such as C++ allows new data types to use the same semantics as built-in numeric types. However, the ELIZA effect can blind one to serious shortcomings when analysing an Artificial intelligence system.
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See also: AI-complete, Turing test