Crispy, Blur is Motorola's enhancement suite for Android. It contains Motorola Home, and all the Motorola apps like the gallery, music player, and widgets. And the stupid lock screen. (I hate Motorola's lock screen. A lot.) HTC's is called Sense and Samsung's is called TouchWiz. They all have one. Very few Android phones are straight-up Android.
Bloat is anything on top of AOSP (Android Open Source Project) and the Google apps. This includes Blur/Sense/TouchWiz, technically, though most don't consider those bloat. If you have US Cellular, City ID is the epitome of bloat. It doesn't work as advertised, it's always there, and it will nag you to pay for it sometimes. Bloat on US Cellular phones also includes Tone Room Deluxe, Your Navigator Deluxe, My Contacts Backup, and the QuickOffice demo. Sprint has a whole other set of bloat apps.
Bricky -- So I don't need bootstrap? Or I do?
Crispy again: On your home screen, hit Menu, Settings, and then About Phone. Near the bottom look for "Android version". If it says 2.3.4 below, you can unlock your bootloader. If it says 2.3.5, you cannot.
Samsung Galaxy S3 / US Cellular / stock 4.1.1