Does "filling out" equal to "filling in"?

I quoted the following from a pamphlet:

Please read the instructions carefully before filling out the application form. The application will be returned to you and the registration may be delayed, if the information is not filled in completely.

Does "filling out" equal to "filling in"?

The words in and out have opposite meanings, how can they produce almost equal meaning in these phrases filling in and filling out?

Solution 1:

Not quite - you fill out a form by filling in your information; on the other hand, the individual boxes can also be filled in.

So it's "fill out" for the whole form; "fill in" for the individual fields and for the information that goes in them.

"Filling out" can also be used in a human-developmental sense; a grandmother might say of her granddaughter whom she hadn't seen in a long time "My, you're filling out nicely, aren't you?" However, when applied to human beings this has a connotation of ripening or sexual maturation, and so it would be extremely creepy in most contexts other than the grandma/grandkid scenario. Edit: as @Jackson Pope reminded me, "filling out" can also mean "gaining weight"; however, I would still be very careful using this to refer to (for instance) a significant other, as it might lead to a night on the couch.

"Filling out nicely" can also be used to refer to team rosters, music festival lineups, etc. - things which start out empty but must be filled to be useful. - Pitchfork Music Festival Filling Out Quite Nicely

One can also "fill in" for another person; that is, take over their duties while they are absent or unavailable: Bundy fills in for LA third-base coach Wallach

Solution 2:

I would say that "fill out" would mean to fill in all (required) fields in the form and complete it. On the other hand, "fill in" would mean to fill in values in some fields in a form (not necessary complete the form).