What is Adblue diesel exhaust fluid?

Adblue is an additive used in many newer diesel cars and has lately made news for being in short supply. So what is it and what does it do?

Valeo Adblue Diesel Exhaust Fluid 10L 004989042012 0005830107 83190441139 G052910A2 716600

Custom Quality Guarantee AdBlue® Diesel Exhaust Fluid AUS32 For EURO 5 EURO 6,Quality Guarantee AdBlue® Diesel Exhaust Fluid AUS32 For EURO 5 EURO 6 Manufacturer,Quality Guarantee AdBlue® Diesel Exhaust Fluid AUS32 For

Diesel Exhaust Fluid Volkswagen AdBlue, 1.89L - G052910A2OE - Pro Detailing

RahaBlue - Diesel Exhaust Fluid - LubeJunction

PRO 99 AdBlue Diesel Exhaust Fluid 10L

Custom AdBlue® Diesel Exhaust Fluid Urea Solution 5L With Integrated Pouring Cover,AdBlue® Diesel Exhaust Fluid Urea Solution 5L With Integrated Pouring Cover Manufacturer,AdBlue® Diesel Exhaust Fluid Urea Solution 5L With Integrated Pouring

Level Sensors for AdBlue/Diesel Exhaust Fluid

AdBLUE DIESEL EXHAUST FLUID (DEF) 10liters

Adblue 20 Litre, Diesel Exhaust Fluid (DEF)

Valvoline Adblue Diesel Exhaust Fluid 20L, Automotive Superstore

What is Adblue, what does it do, how much is it and does my car need it?