"Elegy Written in a Country Churchyard" is written in heroic quatrains. A quatrain is a four-line stanza. Heroic quatrains rhyme in an abab pattern and are written in iambic pentameter. An iamb is a poetic foot consisting of one unstressed and one stressed syllable, as in the phrase "the world." Pentameter simply means that there are five feet in each line. Consider, for instance, the first line of Gray's "Elegy Written in a Country Churchyard":

The Curfew tolls the knell of parting day.

When we scan the line, or identify its stresses, it appears as follows:

TheCur / few tolls / the knell / of part / ing day.

Try reading the line aloud: its regular, steady rhythm helps to creates a calm and quiet mood— one appropriate to the meditative nature of this poem.