What is it called when the first line of a poem rhymes with the fourth line and the second and third lines rhyme?

It is called Rhyme Scheme ( type: enclose rhyme).

Rhyme is the repetition of sounds in a word used for example at the end of lines of poetry, within a word, in songs, etc.

So as a consequence, Rhyme Scheme is the pattern of rhymes, for example at the end of a poem. They are representing by using letters of the alphabet so that each rhyme in a poem that rhyme with other has assigned a letter (starting with the letter 'A').

Enclose rhyme or enclosing rhyme is the rhyme scheme ABBA. For example:

"Love had us mesmerized under its magic spell        A

Our youth's enchanted vision of what life would be        B    

Innocent intentions that let our lives feel free       B

Enraptured in each other's arms as twilight fell."        A

b.science

explanation: