Stress is the emphasis that falls on certain syllables and not others; the arrangement of stresses within a poem is the foundation of poetic rhythm. The process of working out which syllables in a poem are stressed is known as scansion; once a metrical poem has been scanned, it should be possible to see the metre.
By way of example, the word "produce" can be pronounced with the stress on either syllable - a farmer may proDUCE carrots, which a greengrocer will sell as PRODuce. Similarly, the differently placed stress is what separates the English and American pronunciations of "defence".
Longer words may have more than one stress - "photography", for example, is stressed on both '-tog-' and '-phy'. In some places, including the Oxford English Dictionary, a difference is drawn between the primary stress - the heavier emphasis on '-tog-', in this case - and secondary stress, as in the more lightly stressed '-phy'. For the purposes of scansion, however, it is usually enough to consider stress as either present or absent.
However, the different weights of stress mean that its presence or absence is relative - one difference between "a photograph taken on forestry land" and "a photograph composed beneath the trees" is that the second seems to have a stress on the '-graph' syllable that the first lacks. This is because the following syllable is more stressed than '-graph' in the first phrase, but less so in the second.
As English is a language that has stresses in it, every poem in the Archive has stresses in it. Useful examples include Sebastian Barker's reading of 'The Articles of Prayer', which makes strong distinctions between his stressed and unstressed syllables, and draws attention to their patterning, and Sylvia Plath's delivery of 'Parliament Hill Fields' also has clear stresses, but are distributed according to free-verse rhythms.