The whole word, un-hyphenated, un-spaced and spelled as-is, is a critically important form of electronic social expression dating as far back as the early 1990's. The word is a combination of the English word, "Friends," joining the number four (shorthand of "for") and offering the comical substitute, "lyfe" instead of, "life." The "Z" used at the end of "friend" is a common electronic form to add value. Using the "y" in "life" also represents a person's knowledge and appreciation for e-slang while advocating a sarcastic undertone. The greater means of this technique is to emphasize ones commitment to their friends, forever and ever.
"Dang girl, you know we friendz4lyfe!"
"We were roomies, so now we're friends4lyfe..."
"Thanks for the shout! We friends4lyfe kid!"