Imagery in poetry is what the words of the poem make the reader 'see' in their imagination. it is the colors, sounds, and sometimes feelings evoked by the poem.

Ex: The winter evening settles down

With smell of steaks in passageways.

Six o'clock.

The burnt-out ends of smoky days.

And now a gusty shower wraps

The grimy scraps

Of withered leaves about your feet

And newspapers from vacant lots;

The showers beat

On broken blinds and chimney-pots,

And at the corner of the street

A lonely cab-horse steams and stamps.

And then the lighting of the lamps

T.S. Eliot

Imagery is important because

poetry is all about inspiring feelings and conveying a message. Imagery is a great way to get readers to visually manifest your ideas in their head, which gets them much more involved in the reading of your poem.