Definition:
Inventive spelling: Inventive spelling refers to children using incorrect and unusual spellings for words. Typically, inventive spelling is used by students who are just learning to put sounds together to make words. The written form of a inventively-spelled word often will contain the letters of the sounds a child hears when he says a word. In fact, you may hear teachers say to a child who asks how to spell a word "Write the sounds you hear."
Many teachers allow students to use inventive spelling as a way to express their thoughts without having to worry about form or format. The thought is that students will begin using the correct spelling for words once they've built up a better core word vocabulary and a have a stronger sense of letter-sound correspondence.