What is a "custodial account"?

I am attempting to fill out my 2014 tax return, in particular form 9838. There is a distinction between “deposit accounts” and “custodial accounts” that is not, as far as I can tell, addressed either in the form or the instructions, both of which use the terms as though they are well known and obvious. But the terms mean nothing to my wife and me. Can anyone enlighten me? Why are they important?

A custodial account is an account you have for someone else’s benefit - most obviously a minor. So a savings account for a kid, which has to be in the name of someone of the age of majority as well as the child.

There can be tax implications.