Wiktionary
iambic tetrameter
n. A poetic meter consisting of a line with four feet in each of which the iamb is dominant.
Wikipedia
Iambic tetrameter
Iambic tetrameter is a meter in poetry. It refers to a line consisting of four iambic feet. The word " tetrameter" simply means that there are four feet in the line; iambic tetrameter is a line comprising four iambs.
Some poetic forms rely upon iambic tetrameter: triolet, Onegin stanza, In Memoriam stanza, long measure (or long meter) ballad stanza.