Walter Bright's use of the word "redundancy"... or 'The heck does that mean?'

Question

So I'm reading this interview with Walter Bright about the D language in Bitwise (http://www.bitwisemag.com/copy/programming/d/interview/d_programming_language.html), and I come across this really interesting quote about language parsing:

From a theoretical perspective, however, being able to generate a good diagnostic requires that there be redundancy in the syntax. The redundancy is used to make a guess at what was intended, and the more redundancy, the more likely that guess will be correct. It's like the English language - if we misspell a wrod now and then, or if a word missing, the redundancy enables us to correctly guess the meaning. If there is no redundancy in a language, then any random sequence of characters is a valid program.

And now I'm trying to figure out what the heck he means when he says "redundancy".

I can barely wrap my head around the last part, where he mentions that it is possible to have a language in which "any random sequence of characters is a valid program." I was taught that there are three kinds of errors: syntactic, run-time, and semantic. Are there languages in which the only possible errors are semantic? Is assembly like that? What about machine code?