Now somebody gave us a bit of a lesson as some of us , including me, usually say seagull instead of gull! So smarty pants told us that there's no sea around us and to remember it that way.
If you look this up you find that seagull is informal and gull is the proper term as there are many species of gull. So there!
As a little guy I spelled seagull as "seagle" as in eagle. Now that goes too far and is just plain wrong even if you are in gr. two.
There are many other situations where we have a formal usage and an informal usage. So if we are writing in a formal style we would use the formal term.
So do you have examples of formal and informal terms?