Back filling usually refers to replacing the dug out soil into the hole when planting, after putting the plant in place - not sure quite what you want to know otherwise, your question is non specific and too general, requiring a dissertation for a full answer...

just woundering on the differant types of backfilling materials e.g. top soil, sand, pebbles... but sure theres more.

Well I don't mind answering questions, but this one's a bit too general - is it for an exam?

just for work that is all.

The trouble is, any backfill material used for plants is either just ordinary soil, or may have other things added to it, but always based around the requirements of the plant. So it varies between plantings.

Sounds like an exam or homework question to me. It would require an essay to answer it properly.

Plus a definition of what is meant by "backfill" in this instance, Ryan. Bamboo has the normal definition for gardeners, but the word is also occasionally used other ways in gardening, too. What sort of situation are you referring to, anyway? Planting a plant--shrub, tree, etc.? Preparing a garden bed? Building a raised bed and/or retaining wall? We do need more info to answer your question properly.