As far as I know, « Stressed » means « Stress » . Cambridge dictionary have defined the stress as: a word or syllable pronounced with greater force than other words in the same sentence or other syllables in the same word, or a musical note is played with greater force than others in a group. That is you make more effort to produce (or articulate) the sound stressed. For example: In the word “table” /ˈteɪ.bl ̩/ the stress is in the primary position. Note that in “but” /bət/ the /ə/ is never stressed.