"Eschew obfuscation", also stated as "eschew obfuscation, espouse elucidation", is a humorous fumblerule used by English teachers and professors when lecturing about proper writing techniques.
Literally, the phrase means "don't be unclear, be clear", but the use of relatively uncommon words causes confusion, making the phrase an example of irony, and more precisely a heterological or hypocritical phrase (it does not embody its own advice).