When people say "mild steel" are they refering to mild steel or is there a number to it? I looked up online for mild steel and can't find it.
Is it under cold rolled or anything like that?
Mild steel is a general term. Cold rolled steel C1018 is mild steel, hot rolled steel is mild steel, leaded steel C10L14 is mild steel. Here is a definition of mild steel.
Carbon steel is sometimes referred to as 'mild steel' or 'plain carbon steel'. The American Iron and Steel Institute defines a carbon steel as having no more than 2 % carbon and no other appreciable alloying element.
Steel with between .3% and .8% carbon is Medium carbon steel and above .8% it is High carbon.
If the steel has other alloying elements such as manganese or cobalt, etc., it is called alloy steel and if it has chromium it is called stainless steel.