What is this process called?

Apple Time Machine software seems to backup in increments.

So you do your first full TM backup and then after that the initial backup seems to be "built upon" with new data.

But, in data storage terms what is this called? Is it incremental backup?

And secondly, when doing a restore from TM. These "chunks" have to knitted together again. What is this process called?

From a user perspective Time Machine seems easy, but I think behinds the scenes its a lot more convoluted than people think. Can anybody shed some light on what goes on with Time Machine behind the scenes?

Yes, you can call this a form of incremental backup.

And no, contrary to an "traditional" incremental backup, there's no need to "knit together" chunks when restoring. So there's no process that needs to be named here. This is similar to what some vendors name "reverse incremental backups".

An traditional incremental backup system works by first taking a full backup, and then for the following backups storing the changed parts separately - requiring a recombination step when restoring.

Time Machine instead uses a system where you can always directly read out the total backup in its latest form. In rought terms this is done by having a folder for each backup, and in this folder you have every file as it was when this backup was taken. However most of the files share their data contents with files in older backup folders on the drive (via hard links). Some vendors call this a "synthetic full backup".