in poetry poems have different number of lines, what is the name given to poems that have only 4 lines?

The name given to poems that have only 4 lines is stanza.

Explanamtion:

A stanza is a group of lines that form the basic metric unit in a poem. In other words, a stanza is nothing more than a variable set of verses, separated from other similar sets by some punctuation and or a blank space in the poem.

Today poetry does not limit the number of stanzas that a poem can have, but in ancient times lyrical writing was governed by very concise rules, for example, a sonnet is necessarily composed of four stanzas: two of four verses and two of three, with precise rhythmic and syllabic structures.

The stanzas can be classified according to the number of verses they present.

The stanzas that present two verses are known as couplet, elegiac or joyful, according to their specific composition. The stanzas with three verses can be called solea, third or third. The stanzas of four verses, meanwhile, may belong to the qualification of quartet, quartet, couplet or round.

Quintilla, double quintilla, quintet lyre, sixth (stanzas of six verses), compound (seven verses), eight royal (stanzas of eight verses), tenth (ten verses) and sonnet (stanza of fourteen verses) are other types of stanzas.