"Foregrounding," in literary works, means calling special attention to something so that it stands out and is particularly emphasized (see the excellent definition cited below for a much fuller explanation).
A clear (but extreme) example of foregrounding appears in the first two stanzas of Lewis Carroll's famous poem "Jabberwocky":
Twas brillig and the slithy toves
Did gyre and gimble in the wabe,
All mimsy were the borogroves
And the mome raths outgrabe.
Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jub Jub bird
And shun the frumious bandersnatch!
In this example, foregrounding is much more heavily used in the first stanza than in the second. The first stanza calls extreme attention to itself because almost all of the key words are invented. We can recognize which words must be nouns, which must be verbs, and which must be adjectives, but we cannot decipher the precise meaning of any of the language.
In the second stanza, deciphering meaning is a bit easier because more of the words are familiar. These more familiar words include "Beware," "my son," "shun," and "bird." The entire second line is also perfectly clear in meaning and phrasing.
Thus, by the standards of this poem, the first stanza uses "foregrounding" far more than does the second, although by the standards of most poems, the second stanza also uses foregrounding to an unusual degree.