To save me explaining over and over! Here are the versions numbers of Android, and their associated code names

Cupcake 1.5 (No longer supported with Security Patches)
Donut 1.6
Eclair 2.0-2.1
Froyo 2.2-2.2.3
Gingerbread 2.3-2.3.7
Honeycomb 3.0
Ice Cream Sandwich 4.0-4.0.4
Jelly Bean 4.1-4.3.1
KitKat 4.4-4.4..4
Lollipop 5.0-5.1.1 (Still Supported with Security Patches)
MarshMallow 6.0-6.0.1
Nougat 7.0-7.1.2
Oreo 8.0-8.1

Pie 9.0 (Latest Production Version)