The guy above (2 up) is right but I thought I d try and simplify it a bit
Is a set of sort of guidlines that it is set to look for for example if your database was on cars you could create a query to look up cars only that were created between 1999 - 2009 the query would sort through your database and pull out cars that matched this figure. (Applied)
(Doesn't have to be a figure could be text)
A form links in with a query to display information to the user.
You can run a query without a form but it looks plain if you combine it with a form you can print multiple query results on one page.
For example with the car database you could print cars names make model and color all on one form but with multiple querys.
A query sorts information out and pulls out relevant information as set by you the user.
A form is a method of displaying information regardless of the source you can use tables querys etc a form just displays information thats all.