"Eggcorn" is the new informal term, coined by some linguists, for words that people have, essentially, gotten wrong; but which do make some semantic sense in their new ("wrong") version. The term came about because someone once referred to the little things that grow on oak trees as eggcorns rather than the proper acorns - if you didn't know how to spell "acorn," but had heard it spoken, you might assume that the word was "eggcorn," since they are sort of kernel-like and egg-shaped.
Some examples we've all seen on LJ and elsewhere:
"take another tact" (instead of "tack")
"throws of passion" (instead of "throes")
"say one's peace" (instead of "piece")
"peak one's interest" (instead of "pique")
"intensive purposes" (instead of "intents and purposes")
"baited breath" (instead of "bated")
"beckoned call" (instead of "beck and call")
Other examples from their list I haven't seen before, but which particularly amuse me:
"in lame man's terms" ("in layman's terms")
"doggy dog world" ("dog-eat-dog world")
"Cadillac converter" ("catalytic converter")
"spread like wildflowers" ("spread like wildfire") (That one I actually like.)
Naturally, the reason some of these phrases have been reinterpreted, and re-spelled accordingly, is that the original terms are not in common use - e.g., the rather antique "beck," "throes," and "bated"; along with any jargon particular to a certain discipline, such as the sailing-related "tack" in "take a different tack." Others, though, I can't account for, and I think the linguists are being generous in calling them "eggcorns" rather than simply "malapropisms."
Still, I have to admit that I would have said "anchors away!" without realizing the original term was "anchors aweigh." Now that I think about it, though, you really wouldn't leave the anchors behind, so "away" doesn't make any sense.