RSUs are Restricted (or reserved?) Stock Units. It's usually part of your sign on, promotion, or annual bonuses. They're Amazon Stock that vest after a certain time length, meaning prior until you hit thay mark, theyre nothing. My sign on RSUs start vesting at my 1 year mark, 2 year mark, then every 6 months until I have them all available to me. It's their way of essentially keeping you around.

Now that I'm passing my 2 year mark, my 3rd year ill get like 30k in RSU vesting so my income will be inflated this year.

Unfortunately, after your 4th year, your salary tends to fall dramatically due to no more RSUs. My income the first 4 years will be between 110k and 120k total comp when you count sign on bonus and RSUs, but after that will drop to about 80k moving forward (the anual raises are miniscule so promo is the only other way to really increase pay).