Using the first letter of each word to create a word?
A 2017 example of a full word acrostic poem using the first word of every line, entitled "For 2/14": 
What is the poem called when using the first letter of each word to create a word?
Acrostic
Acrostic
Whereas an abbreviation may be any type of shortened form, such as words with the middle omitted (for example, "Rd" for "road" or "Dr" for "Doctor"), an acronym is a word formed from the first letter or first few letters of each word in a phrase (such as "sonar", created from "sound navigation and ranging"). Attestations for "" in German are known from 1921, and for "acronym" in English from 1940.
What is it called when you use the first letter of each word to create a word?
Acronym
Acronym
Acronym
https://en.wikipedia.org/wiki/Acronym
Acrostic
https://en.wikipedia.org/wiki/Acrostic
Acronym is a word formed from the first letter or first few letters of each word in a phrase. The poem that is formed when using the first word of each line to create a word is called an Acrostic poem.