A trochee is a foot used in metered poetry consisting of two syllables. Instead of being short-long like an iamb, a trochee is long-short. When the trochee is used as a substitution in iambic poetry, it helps the syllables to stand out and be emphasized.
Example Absalom and Achitophel, (501-505):
The next for interest sought to embroil the state,
To sell their duty at a dearer rate;
And make their Jewish markets of the throne;
Pretending public good, to serve their own.
Others thought kings a useless heavy load,
Here the word others comprises a trochee. The trochee highlights that the topic is changing, so that the reader doesn't get confused.
Robert Martin, 1B