Meter is the pattern of stressed and unstressed syllables in lines of poetry with a specific number of syllables. Iambic, tetrameter and trimeter are types of meter.
Iambic describes two syllables together following a pattern of unstressed then stressed. For example, the words "when in" are used and the word "in" is stressed.
Tetrameter is the term used to describe the number of iambic patterns in one line. Each pattern is called a foot. In iambic tetrameter, each foot is made up of two syllables, and each line contains four feet.
In iambic trimeter, each foot contains two syllables, and a line is made up of three feet.
A rhyme scheme is a consistent pattern of rhymes throughout a poem. The scheme used in ballad meter is one where the second and fourth lines rhyme. The pattern can be represented as: A-B-C-B, where each "B" represents a rhyming line.
Ballad meter is a type of poetry that uses alternating lines of iambic tetrameter and iambic trimeter, with a rhyme scheme of A-B-C-B.