Poems are, of all kinds of writing, reliant on their use of form. Form means shape and sound, so this means that poets always use both the shape and the sounds of language to help add to the meaning or feeling the poem creates.
Metre is the technical way to describe and label the shape and sound each line of poetry has. It is a way of describing the rhythm contained within the lines.
A highly metrical poem not only has a regular and repetitive beat throughout each of its lines but it will also display a regular shape. The effect of these two things is often to hint at, perhaps, a sense of formality, or rigidness or even a sense that "all is well with the world".
A loosely constructed poem is one that is not reliant on repeating metrical units and this kind of poem is described as free verse, or vers libre. This is more common from the First World War onwards and might be seen to suggest a lack of control over the events of life.
You can work out the metre of a line of poetry by searching for the most frequently repeated unit within each line. This is done by counting the stressed beats within the line. You will find some syllables are stressed and spoken more loudly and others are unstressed and spoken softly. If these stressed syllables occur in repeating units, these are given names according to the pattern of repetition.
The names are rather odd sounding as they are derived from ancient Latin. Two of the most frequently found are called iambic and trochaic rhythm. Each repeated unit which usually consists of two or three syllables is called a foot.
An iambic foot consists of two syllables with the second being stressed; a trochaic foot is the reverse of this, two syllables with the first being stressed - if you speak your name, if it is two syllables, you will speak it as a trochaic foot. Trying to give a person's name iambic rhythm is virtually impossible - try it!
The number of repeated units in a metrical line also needs to be stated, for example, if there are five repeated units this is called a pentameter (using the Latin prefix penta- meaning five, as in 'pentagon'; a tetrameter has four repeating units and so on. Notice also the confusing spelling change from metre to meter!).
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