What is the difference between an Incremental and a Differential Backup?

A lot of these answers are missing with 'what this means for you'

Incremental: backs up changed files since last backup. This means to do a Full restore, you need the last full backup, and every Incremental since.

Differential: Backs up changed files since last FULL backup. Backups are bigger then incremental, but to do a Full restore, you need the last full backup, and the last Differential. You don't need the ones in between.

Typically, a differential backup provides a backup of files that have changed since a full backup was performed. An incremental backup provides a backup of files that have changed or are new since the last incremental backup.

For more information read this article from Microsoft on Full, Incremental, and Differential Backups or the Wikipedia's description:

Incremental

A "normal" incremental backup will back up only those files that have been changed since the last backup of any type. This provides the quickest means of backup, since it makes copies only of files that have not yet been backed up. For instance, following a full backup on Friday, Monday’s tape will contain only those files changed since Friday. Tuesday’s tape contains only those files changed since Monday, and so on. The downside to this is that in order to perform a full restore, one needs to restore the last full backup first, followed by each of the subsequent incremental backups to the present day in the correct order. Should any one of these backup copies be damaged (particularly the full backup), the restore will be incomplete.

Differential

A cumulative backup of all changes made since the last full or normal backup, i.e., the differences since the last full backup. The advantage to this is the quicker recovery time, requiring only a full backup and the last differential backup to restore the system. The disadvantage is that for each day elapsed since the last full backup, more data needs to be backed up, especially if a significant proportion of the data has been changed.