Metre in a literary piece refers to the pattern of stressed and unstressed syllables in a line of poetry. It is what creates the rhythm of the poem.
When we read a poem out loud, we naturally emphasize certain syllables more than others, and the pattern of these emphasized syllables is what creates the metre. For example, in the line "The rain in Spain stays mainly in the plain" from the musical My Fair Lady, the stress falls on the first syllable of "rain," the second syllable of "Spain," the first syllable of "mainly," and the second syllable of "plain."
The metre of a poem can be regular or irregular, depending on the poet's intentions. For example, a poem written in iambic pentameter has a regular pattern of ten syllables per line, with the stress falling on every other syllable. In contrast, a free verse poem has no regular pattern of stressed and unstressed syllables, allowing the poet more flexibility and creativity in their writing.
In summary, metre in a literary piece refers to the pattern of stressed and unstressed syllables in a line of poetry, which creates the poem's rhythm.