A phenomenon where the relative pronoun and the verb "to be" are removed from certain relative clauses.
Whiz-deletion is a type of ellipsis which removes the relative pronoun and the verb be from certain relative-clauses.
The schoolyard was noisy with children who were running around. [explicit]
The schoolyard was noisy with children
who wererunning around. [reduced by whiz-deletion]
The term is a humorous reference to the fact that most relative-pronouns start with wh (who, which, etc.) and that is is a very common for of be, hence wh + is deletion.
