What is the difference between Armor/Attack Damage and Bonus Armor/Attack Damage

I've noticed that some skills or items scale on bonus Attack Damage, while others scale on Attack Damage

There are equivalent items for Armor for example.

Is it something to do with the items? ie if my base AD is 100 and I have no items other than one BF Sword (50 AD), my AD will be 150, but my Bonus AD will be 50? Or is there some other factor at play here?

Base stats are the stats your champion gets as a function of level, i.e. the level 1 base + increase per level.

Bonus stats are all stats you get that are not base stats, i.e. runes, masteries, items, your skills, and buffs from other sources such as team mate auras.

Total stats are the sum of both.

If anything asks about a stat without the base/bonus qualifier, it always means the total stat.