A poetry collection is often a compilation of several poems by one poet to be published in a single volume or chapbook.
Typically the poems included in single volume of poetry, or a cycle of poems, are linked by their style or thematic material.
Most poets publish several volumes of poetry through the course of their life while other poets publish one (e.g. Walt Whitman's lifelong expansion of Leaves of Grass).
The notion of a "collection" differs in definition from volumes of a poet's "collected poems", "selected poems" or from a poetry anthology.
[1] Comparatively, a volume titled "selected poems" often includes a small but not definitive selection of poems by a poet or editor drawn from several of the poet's collections.