It refers to a line consisting of four iambic feet.

Analyzing this, a poet would see a couplet with four iambic metrical feet in the first line and three in the second.

Iambic tetrameter is a meter referring to a line consisting of four iambic feet:

Iambic Pentameter is a meter referring to a line consisting of five iambic feet:

Iambic Heptameter is a meter referring to a line consisting of seven iambic feet:

Each line is a fourteener, having fourteen syllables and seven iambic feet.

Usually associated with the comic theatre, it consists of seven feet with an extra syllable at the end instead of a full iambic foot.

The strong syllables of the remaining iambic feet each carry secondary stress, as do any final weak syllables.

An iambic foot is an unstressed syllable followed by a stressed syllable.

A standard line of iambic pentameter is five iambic feet in a row: