A fourteen-line poem traditionally written in iambic pentameter is called a sonnet. The form originated in Italy and became one of the most influential fixed forms in European poetry.
The word “sonnet” comes from the Italian sonetto, meaning “little sound” or “little song.” The Italian poet Petrarch helped establish the form through poems addressed to Laura. Petrarchan sonnets typically divide into an octave of eight lines and a sestet of six, often with a change in thought called a volta between them.
English poets developed their own major pattern. The Shakespearean sonnet uses three quatrains and a final rhyming couplet, commonly following ABAB CDCD EFEF GG. William Shakespeare’s sonnets are usually written in iambic pentameter, meaning five iambs per line: five pairs of an unstressed syllable followed by a stressed syllable.
A useful qualification is that not every sonnet uses iambic pentameter, and some 14-line poems do not follow a strict traditional sonnet pattern. Villanelles have 19 lines, limericks usually have five, and haiku traditionally have three lines, so none is the standard answer here.