In lyric-writing, a line’s rhythm is the distribution of its stresses.
Examples
S = stressed, u = unstressed.
Give her a chance to sing by herself
S u u S u S u u S
Pouring it out, pure and sweet
S u u S S u S
A rising star for all to see
u S u S u S u S
I walked to the store in the rain
u S u u S u u S
I began to notice the signs
u u S u S u u S